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Polynuclear Complexes Containing Ditopic Bispyrazolylmethane
Ligands. Influence of Metal Geometry and Supramolecular
Interactions
M. Carmen Carrión,†,‡ Gema Durá,† Félix A. Jalón,† Blanca R. Manzano,*,† and Ana M. Rodríguez§
†
Departamento de Química Inorgánica, Orgánica y Bioquímica, Universidad de Castilla-La Mancha,
Facultad de Químicas-IRICA, Avda. C. J. Cela, 10, 13071 Ciudad Real, Spain
‡
Fundación PCYTA, Paseo de la Innovación, 1, Edificio Emprendedores, 02006 Albacete, Spain
§
Departamento de Química Inorgánica, Orgánica y Bioquímica, Universidad de Castilla-La Mancha,
Escuela Técnica Superior de Ingenieros Industriales, Avda. C. J. Cela, 3, 13071 Ciudad Real, Spain
S Supporting Information
*
ABSTRACT: The new ligands bis(pyrazol-1-yl)(pyridine-4yl)methane (bpzm4py) (L1) and bis(3,5-dimethylpyrazol-1yl)(pyridine-4-yl)methane (bpz*m4py) (L2) were synthesized
and were made to react with different metallic starting materials.
In the case of Pd(II), chloride or allyl trinuclear complexes were
synthesized, in which the central palladium is bonded to two
ligands through the pyridine moiety. Mononuclear [Pd(allyl)L]X
complexes were also isolated. On using other M(II) centers
(M = Co, Ni, Zn), which could adopt an octahedral geometry,
box-like cyclic dimers formed by the self-assembly of two metal centers and two ligands in a head-to-tail disposition were
obtained. All metal ions exhibited a distorted octahedral geometry. A complex of Ag(I) with similar cyclic dimers connected
through difluorophosphate anions to generate zigzag chains was also crystallized. The silver center was five-coordinate and the
chain interactions gave rise to the formation of sheets. In the solid state, different noncovalent interactions were present in the
molecular and supramolecular structures, including hydrogen bonds, π−π stacking and anion−π or CH−π interactions. Examples
of possible synergy between some of these interactions were found. Where possible, the solution chemistry was analyzed and
correlated with the solid state structure. The existence of polynuclear species in solution was evaluated and the effect of some
noncovalent interactions on the NMR resonances was observed.
■
π−π stacking,11 and cation−π,12 anion−π,13 and XH−π
interactions.14
A judicious selection of the building blocks and how they are
connected allows some control over the final structure of the
MOMs (metal−organic materials). Since most transition metal
connectors are cationic, an anionic source should neutralize the
overall charge. These anions exist as free guests, counterions or
linkers in the coordination polymers and they usually act as
hydrogen bond acceptors through their oxygen or fluorine
atoms and may influence the crystal structure of the material
obtained. Other factors, such as the solvent or other species
that may act as templates, can also affect the structure of the
supramolecule.
A wide variety of metal atoms in their stable oxidation states
have been used in the self-assembly processes and the most
common organic linkers have been polycarboxylic aromatic
molecules and nitrogenated ligands such as bipyridines or other
species containing azaheterocycles.3,4e,15
INTRODUCTION
In recent years significant progress has been made in the
synthesis and characterization of infinite one-, two-, and threedimensional inorganic/organic hybrid networks formed by
the self-assembly of organic and metallic components.1 Among
them, MOFs (metal organic frameworks), which are crystalline
and porous compounds involving strong metal−ligand interactions,2 are receiving particular attention because of their
applications.3 The pores of MOFs are usually occupied by
solvent molecules that must be removed for most applications,
without structural collapse, to generate a permanent porosity.
Applications include gas storage and separation,4 ion exchange,4e,5
catalysis,3,4e,f storage and release of drugs,4f use as semiconductors6 or sensors,7 and also applications related to magnetic2,4f,8
or luminescent properties.4f,6
The key features that influence the architecture of selfassembled species are the building blocks: the metal, which
usually has a preferred coordination environment, and the ligand,
which not only provides the donor atoms situated at specific
positions1a,9 but can also provide potential interaction sites to
generate noncovalent interactions, such as hydrogen-bonding,10
© 2012 American Chemical Society
Received: December 20, 2011
Revised: February 2, 2012
Published: February 9, 2012
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A “two-step self-assembly” methodology has also been
developed and this involves the synthesis of molecular building
blocks that are themselves metal complexes. In this way, a
metalloligand is synthesized initially and this compound is
subsequently added to another metal ion, which acts as a node
in the framework and, consequently, two kinds of metal center
could coexist in a framework.4e,j These metalloligands may
expand the type of connectors available and offer control over
the bond angles and number of coordination sites and could
also allow the possibility of generating longer spacers to modify
the size of the cavity in the case of MOF derivatives.
In recent years, we have synthesized bis(pyrazol-1-yl)methane derivatives that contain a substituent at the methynic
carbon.16,17 These types of derivatives may be classified as
scorpionates (or heteroscorpionates) if they have the ability to
behave as facially coordinating ligands and the chemistry of
these systems has been profusely developed.18 However, if the
position of the donor atom in the third substituent and the
rigidity of the ligand preclude coordination of the three donor
atoms to the same metallic center, the ligand will probably
behave as a bridge. Ligands of this type were reported by
Carrano et al. and these examples involve the use of (4- or
3-carboxyphenyl)bis(pyrazolyl)methane ligands for the synthesis of mononuclear complexes or box-like cyclic dimers of
Cu(II),19 Ni(II), and Co(II),20 which lead to supramolecular
structures through different weak interactions, mainly hydrogen
bonds. Covalently bonded polymeric 1D chains were obtained
by including dicarboxylate ligands to bridge the dinuclear units.21
Dinuclear species or chain-like structures have also been obtained
with other pyrazolyl-containing ligands and Ag(I),22 Cu(II),23
or Au(I).24
Other examples of poly(pyrazolyl)methane ligands that act as
bridges have been described and include systems containing
pyrazolyl-pyridine “arms”25 or the ditopic phenylene- or methylenelinked tris- or bis(pyrazolyl)methane ligands described by
Reger et al. that led to discrete molecules of Pt(II), Re(I),26
or Ru(II)27 and also to bi- or trinuclear or 1D coordination
polymers of Ag(I).28
In the work reported here, we targeted the synthesis of
bis(pyrazol-1-yl)methane ligands with a 4-pyridyl substituent in
the central carbon with the aim of obtaining all-nitrogen donor
ligands for use as connectors between metallic centers or to
obtain metalloligands that could form supramolecular structures by self-assembly. The ligands obtained and the numbering
are represented in Chart 1.
that it has recently been demonstrated that in different systems
there is interplay between ion−π and π−π, CH−π or hydrogenbonding interactions, which can lead to cooperative effects,29,30
possible examples of this synergy were sought in this study.
A comparison between the solid state and solution structure
was also undertaken.
■
EXPERIMENTAL SECTION
General Comments. The synthesis of the ligands and palladium
complexes was carried out under a nitrogen atmosphere using standard
Schlenk techniques, while the rest of the reactions were carried out
in the air. Solvents were freshly distilled from the appropriate drying
agents and degassed before use. Elemental analyses were performed
with a Thermo Quest Flash EA1112 microanalyzer. IR spectra
were recorded on microcrystalline solids with an ATR system on
IRPRESTIGE-21 Shimadzu (4000−600 cm−1) spectrophotometer.
Mass spectrometry measurements were carried out on a matrix assisted
laser desorption ionization-time-of-flight (MALDI-TOF) Applied Biosystems Voyager DE STR system or with a Q-q-TOF hybrid analyzer
with an electrospray ionization source (ESI-TOF) QStar Elite Applied
Biosystems spectrometer. Thermogravimetric analysis (TGA) and
differential thermal analysis (DTA) were made with an ATDTG
SETARAM apparatus with a 92−16.18 graphite oven and CS32 controller. The analyses were made, without applying initial vacuum and
with a heating rate of 5 °C/min, under an air flux in a platinum
crucible.1H, 13C{1H}, 31P{1H}, and 19F{1H} spectra were recorded on
Varian Unity 300, Varian Gemini 400 and Inova 500 spectrometers.
Chemical shifts (ppm) are relative to tetramethylsilane (1H, 13C NMR),
H3PO4/85% (31P NMR) and CFCl3 (19F NMR). Coupling constants
(J) are in Hertz. The NOE difference spectra were recorded with a
5000 Hz spectrum width, an acquisition time of 3.27 s, a pulse width of
90°, a relaxation delay of 4 s, an irradiation power of 5−10 dB, and a
number of scans of 240. For 1H−13C g-HMQC and g-HMBC spectra,
the standard VARIAN pulse sequences were used (VNMR 6.1 C software). The spectra were acquired using 7996 (1H) and 25133.5 Hz
(13C) spectrum widths; 16 transients of 2048 data points were collected
for each of the 256 increments. For variable temperature spectra, the
probe temperature (±1 K) was controlled by a standard unit calibrated
with a methanol reference. In the NMR data, s, d, and b refer to singlet,
doublet, and broad, respectively. The carbon resonances are singlets.
UV−visible spectra were recorded on an Uvikon-XS spectrofluorimeter.
The starting materials bis(pyrazol-1-yl)ketone (bpzCO) and bis(3,5-dimethylpyrazol-1-yl)ketone (bpz*CO),17c PdCl2(PhCN)231 and
[Pd(η3-C4H7)(μ-Cl)]232 were prepared according to literature procedures. The metallic salts CoCl2, Ni(NO3)2·6H2O, Zn(NO3)2·6H2O,
AgBF4, and AgPF6 were purchased from Fluka or Aldrich and were
used without further purification.
X-ray Structure Determination for L2, 2·2Me2CO, 3, 4·Me2CO·
0.5H2O, 7·DMF, 9·2DMF, 10·3DMF, 11, and 13·0.5THF. For all
compounds, the crystal evaluation and data collection were performed
on a Bruker X8 APEX II CCD area detector diffractometer using
graphite monochromated Mo Kα radiation (λ = 0.71073 Å, sealed
X-ray tube). Data were integrated using SAINT33 and an absorption
correction was performed with the program SADABS.34 Far all structures, a successful solution by the direct methods provided most nonhydrogen atoms from the E-map.35 The remaining non-hydrogen
atoms were located in an alternating series of least-squares cycles
and difference Fourier maps. All non-hydrogen atoms were refined
with anisotropic displacement coefficients unless specified otherwise.
All hydrogen atoms were included in the structure factor calculation at
idealized positions and were allowed to ride on the neighboring atoms
with relative isotropic displacement coefficients.
Complex 3 shows disorder for the central allyl group, one pyrazol
and the BF4− counterions and some restraints are used (DELU, SIMU
and FLAT). In the crystal structure of compound 7, two DMF coordinated molecules are disordered over two positions and are modeled
as a 50:50 isotropic mixture. Compounds 3, 7, and 11 crystallize with
some DMF molecules of solvent heavily disordered. Compound 13
crystallize with some acetone molecules disordered. A significant amount
Chart 1. Ligands L1 and L2, Numbering and Abbreviations
Other objectives of this work were to analyze the effect
on the final structure of the type of metal and the anion used by
considering their potential coordination ability and the possibility of hydrogen bond formation. We were also interested in
evaluating the influence of the noncovalent interactions on the
shape of the molecules and the crystalline structure. Considering
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H3+H5-py), 8.09 (s, 1H, Hα), 8.64 (bs, 2H, H2+H6-py) ppm. 13C{1H}
NMR (acetone-d6, 100 MHz, 25 °C): δ = 10.48 (Me5-pz), 14.06 (Me3pz), 20.97 (Me-allyl), 59.76 (CH2-allyl), 68.13 (Cα), 107.6 (C4-pz),
120.9 (C3+C5-py), 150.48 (C4-py), 153.60 (C2+C6-py) ppm. 19F
NMR (acetone-d6, 211 MHz, 25 °C) δ = −151.8 ppm. IR (ATR)
ν/cm−1: 1557 ν(CN); 1047, 1032 ν(BF4−); 1393, 864 (2-Me-allyl).
λmax (MeOH, ε): 222 (33700 M−1 cm−1); 270 (5000 M−1 cm−1).
MS (MALDI-TOF+,SA): m/z (assign., rel. int. %): 442 [Pd(C4H7)(bpz*m4py)+, 100].
[Zn(bpz*m4py)(DMF)(NO3)]2(NO3), 12. Zn(NO3)2 (10.0 mg,
0.03 mmol) and L2 (10.0 mg, 0.03 mmol) were dissolved in DMF
(1 mL) at room temperature. The mixture was stirred for 5 minutes.
By slow diffusion of diethyl ether in gas phase into the DMF solution,
compound 12 was obtained as a crystalline colorless product that was
dried under vacuum. Yield: 11.7 mg, 36%. Anal. Calcd for
C32H38N14O12Zn2·2C3H7NO·H2O: C, 41.28, H, 4.92; N, 20.27.
Found: C, 41.37; H, 4.81; N, 20.40. 1H NMR (methanol-d4, 500
MHz, 25 °C): the resonances of the ligand are broad. Those of the
box-like dimer are the following: δ 2.17−2.20 (bs, 24H, Me3+Me5-pz),
6.35−6.48 (bs, 8 H, H3+H5-py and H4-pz), 8.05 (bs, 2H, Hα), 8.25
(bs, 4H, H2+H6-py) ppm. IR (ATR) ν/cm−1: 1654 ν (CN), 1460,
1309, 1037 (η2- NO3−); 1423, 698 (NO3−). λ max (MeOH, ε): 261
(4253 M−1cm −1); 289 (2310 M−1cm−1). MS (MALDI-TOF+, SA):
m/z (assign., rel. int. %): 501 [Zn2(bpz*m4py)+ + 5H2O, 100], 281
[bpz*m4py, 13].
of time was invested in identifying and refining the disordered
molecules. Bond length restraints were applied to model the molecules
but the resulting isotropic displacement coefficients suggested the
molecules were mobile. Option squeeze of program PLATON36 was
used to correct the diffraction data for diffuse scattering effects. Note
that all derived results in the corresponding tables are based on the
known contents.
X-ray crystallographic information files (CIF) are available for
compounds L2, 2·2Me2CO, 3, 4·Me2CO·0.5H2O, 7·DMF, 9·2DMF,
10·3DMF, 11, and 13·0.5THF.
Syntheses of the New Derivatives. The synthesis of all the new
derivatives described in this paper is included in the Supporting
Information. In the following paragraphs, the synthesis of some representative compounds with NMR data relevant for the Results and
Discussion section is included.
bpz*m4py, L2. bpz*CO (2 g, 9.16 mmol) and 4-pyridinecarboxaldehyde (0.87 mL, 9.16 mmol) were mixed in toluene (30 mL). After
refluxing for 72 h, the yellowish solution was evaporated, and the
residue was washed with pentane (3 × 10 mL), obtaining a white solid
of bpz*m4py. Yield: 2 g, 78%. Anal. Calcd for C16H19N5: C, 68.30; H,
6.81; N, 24.89. Found: C, 68.54; H, 6.73; N, 25.10. 1H NMR (acetoned6, 500 MHz, 25 °C): δ = 2.12 (s, 6H, Me3-pz), 2.22 (s, 6H, Me5-pz),
5.91 (s, 2H, H4-pz), 6.96 (d, J = 4.3 Hz, 2H, H3 + H5-py), 7.77 (s, 1H,
Hα), 8.58 (d, J = 4.3 Hz, 2H, H2 + H6-py) ppm. 13C{1H} NMR
(acetone-d6, 125 MHz, 25 °C): δ = 11.16 (Me5-pz), 13.16 (Me3-pz),
72.73 (Cα), 106.72 (C4-pz), 122.19 (C3+C5-py), 141.40 (C5-pz),
145.92 (C4-py), 148.19 (C3-pz), 150.08 (C2+C6-py) ppm. IR (ATR)
ν/cm−1: 1595 ν(CN). λmax (MeOH, ε): 219 (13970 M−1cm−1); 261
(2526 M−1cm−1). Single crystals suitable for X-ray analysis were
obtained by slow evaporation of a toluene solution of L2.
[Pd3(η3-C4H7)3(bpz*m4py)2](BF4)3, 4. [PdCl(η3-C4H7)]2 (21.0
mg, 0.05 mmol) and AgBF4 (21.0 mg, 0.10 mmol) were dissolved in
acetone (5 mL), and the mixture, protected from the light, was stirred
for 2 h at room temperature. After this time, it was filtered and the
solution added to an acetone (5 mL) solution of L2 (20.0 mg, 0.07
mmol). The reaction mixture was stirred at room temperature for 1 h.
The solvent was evaporated to dryness and the white product dried
under vacuum. Yield: 37.0 mg, 75%. Anal. Calcd. for
C44H59B3N10F12Pd3·0.5C3H6O: C, 41.30; H, 4.80; N, 10.26. Found:
C, 40.95; H, 4.93; N, 10.16. 1H NMR (acetone-d6, 400 MHz, 25 °C):
δ = 1.36 (s, 6H, Me-allylext), 2.24 (s, 3H, Me-allylcent), 2.33 (s, 12H,
Me3-pz), 2.65 (s, 12H, Me5-pz), 3.19 (bs, 4H, Hanti-allylext), 3.28 (bs,
2H, Hanti-allylcent), 3.91 (bs, 2H, Hsyn-allylcent), 4.06 (bs, 4H, Hsynallylext), 6.37 (s, 4H, H4-pz), 6.76 (d, J = 4.9 Hz, 4H, H3+ H5-py), 8.00
(s, 2H, Hα), 8.67 (d, J = 4.9 Hz, 4H, H2+ H6-py) ppm. 13C{1H} NMR
(acetone-d6, 100 MHz, 25 °C): δ = 10.21 (Me5-pz), 13.70 (Me 3-pz),
20.70 (Me-allyl ext), 22.63 (Me-allylcent), 60.02 (CH2-allylext), 60.95
(CH2-allylcent), 67.59 (Cα), 107.64 (C4-pz), 123.58 (C3+C5-py),
132.42 (C-allylext), 135.94 (C-allylcent), 145.24 (C5-pz), 148.09 (C4py), 152.61 (C2+C6-py), 154.07 (C3-pz) ppm. 19F NMR (acetone-d6,
211 MHz, 25 °C) δ = −150.9 ppm. IR (ATR) ν/cm−1: 1558 ν(C
N); 1049, 1035 ν(BF4−); 1392, 867 (2-Me-allyl). λmax (MeOH, ε): 222
(79480 M−1cm−1); 285 (7840 M−1cm−1). MS (MALDI-TOF+,SA):
m/z (assign., rel. int. %): 442 [Pd(C4H7)(bpz*m4py)+, 100].
Colorless crystals of 4·Me2CO·0.5H2O, suitable for X-ray diffraction,
were obtained by slow diffusion of diethyl ether in gas phase into an
acetone solution of complex 4.
[Pd3(η3-C4H7)(bpz*m4py)](BF4), 6. [PdCl(η3-C4H7)]2 (25.0 mg,
0.06 mmol) and AgBF4 (25.0 mg, 0.12 mmol) were dissolved in
acetone (5 mL), and the mixture, protected from the light, was stirred
for 2 h at room temperature. After this time, it was filtered and the
solution added to an acetone (5 mL) solution of L2 (70.0 mg, 0.25
mmol). The reaction mixture was stirred at room temperature for 1 h.
The pale solution was evaporated under vacuum and the residue was
washed with ether (3 × 4 mL) obtaining the complex as a white
powder. Yield: 41.0 mg, 61%. Anal. Calcd for C20H26BN5F4Pd·
0.5H2O: C, 44.60; H, 5.05; N, 13.00. Found: C, 44.47; H, 4.55;
N, 12.63. 1H NMR (acetone-d6, 400 MHz, 25 °C): δ = 1.37 (bs, 3H,
Me-allyl), 2.35 (s, 6H, Me3-pz), 2.72 (s, 6H, Me5-pz), 3.12 (bs, 2H,
Hanti-allyl), 4.02 (bs, 2H, Hsyn-allyl), 6.41 (s, 2H, H4-pz), 6.65 (bs, 2H,
■
RESULTS AND DISCUSSION
Synthesis and General Characterization of the
Ligands. The ligands used in this work, bpzm4py (L1) and
bpz*m4py (L2), were synthesized in good yield by following a
green methodology developed in our research group for the
synthesis of substituted bis(pyrazol-1-yl)methane ligands. This
approach involves the use of solid triphosgene instead of the
previously reported and more volatile phosgene.17c The intermediate ketone derivatives bis(pyrazol-1-yl)ketone (bpzCO) or
bis(3,5-dimethylpyrazol-1-yl)ketone (bpz*CO) were reacted with
pyridine-4-carboxaldehyde in refluxing toluene (Scheme 1).
Scheme 1. Synthesis of L1 and L2
The 1H NMR spectra of these ligands show that both pyrazolyl
groups are equivalent and NOE effects, observed between Hα
and H3/5 of the pyridine ring and also with H5/Me5 of the
pyrazolyl rings, confirm the formation of the new compounds.
The structure of ligand L2 was determined by X-ray diffraction
(see solid state characterization).
Synthesis and General Characterization of the New
Metallic Derivatives. The ligands L1 and L2 can be
schematically represented as shown in Chart 2. If we consider
the possible products that can be formed by reaction of these
ligands and a square-planar metal center with two accessible
coordination sites, some coordination alternatives are represented in Chart 2 for different M:L stoichiometries. In structures I, II, and III, which involve chelate coordination through
the pyrazole rings (I) or monodentate coordination via the
pyridinic nitrogen (II, III), some ligand donor atoms remain
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Chart 2. Schematic Representation of Ligands L1 and L2 and Some Hypothetical Species That Could Be Formed by Reaction
with Square-Planar Metallic Centers
Zn(II), and Ag(I) derivatives were performed as described
below.
The reaction of ligands L1 and L2 with PdCl2(PhCN)2 was
initially performed with Pd:L ratios of 1:1 and 1:2 to assess the
possibility of obtaining mononuclear complexes of type I or II,
respectively.
Very insoluble derivatives were obtained and elemental analysis data were not consistent with the expected stoichiometries.
The 1H NMR spectra had to be recorded in DMSO-d6 and a
complex set of broad signals was obtained, possibly due to
interchange processes between different species that could even
involve the solvent. As a result, the isolation of crystals was
targeted and those obtained had the stoichiometry Pd/L =
3:2. The same crystals were obtained on reacting the starting
materials in a 3:2 ratio. On the basis of steric requirements, the
most reasonable structure for the new derivatives 1 and 2 is IV,
in which the central palladium atom has a trans disposition (see
Scheme 2).
Considering the formation of these products, we decided
to analyze the possible formation of a structure of type V, in
which an ancillary ligand forces a cis disposition in the central
palladium center, as well as the possibility of forming structures
of type I or III. Thus, the reactions of ligands L1 or L2 with the
allyl-solvate derivative generated in situ, that is, [Pd(η3-C4H7)(acetone)2]BF4, were performed with different Pd/L ratios
(Scheme 2). On employing a 1:1 ratio the main products
obtained, after purification of the corresponding solid, were
the trinuclear derivatives 3 and 4 (from ligands L1 and L2,
respectively) with a structure of type V. These compounds
were better obtained using a Pd:L ratio of 3:2. To obtain the
mononuclear derivatives 5 and 6, with a structure of type I, an
excess of ligand (1:2 ratio) was necessary. Species of type III
(with two ligands) were not detected.
The structures of 2, 3, and 4 were determined by X-ray diffraction (see below), and their trinuclear nature was confirmed.
Reaction of the ligands L1 and L2 with other M(II) centers
(M = Co, Ni, Zn) (M/L = 1:1) with at least three accessible
coordination sites gave box-like cyclic dimers with an M/L ratio
of 1:1, reflecting a structure of type VI (Chart 3). The derivatives obtained (7−12) are shown in Scheme 3. In the case of
complexes 7, 9, 10, and 11 the structures were determined by
X-ray diffraction (see below) and the ancillary ligands are those
included in Scheme 3. Anions are present to achieve electroneutrality and, in some cases, one is coordinated to each metal
center. It is interesting to note that in the case of 7 a [CoCl4]2−
complex per dimer is present as counteranion, a fact that
explains the intense blue color of the complex. Complex 8 is
that are not coordinated to the metal and the formation of
supramolecular species through coordination to other centers
could be possible. In fact, it must be stated that, unless the
coordinaton to another metallic center takes place, the adoption
of structures II and III, in which the chelate system remains
uncoordinated, is not very probable. Only four of the several
hundreds of structures reported to contain a bis(pyrazolyl) moiety
and a third donor atom in a group bonded to the central carbon
atom exhibited one uncoordinated pyrazolyl fragment.16a,37
In contrast, in IV and V the M:L ratio of 3:2 means that the
number of metal coordination sites and donor atoms of the
ligands are the same and thus all donor atoms are coordinated.
When an anti or syn orientation of the two ligands is possible
in the complex (e.g., II−V) the anti orientation, which would
involve a lower steric requirement, is shown in the figure. It is
interesting to note that in structure IV, in which the metal
centers are in two different environments, the two external
centers have the same structure as in I and the central metal
center is similar to that in II. The same applies for V, which has
similarities with I and III.
If the reaction of ligands L1 and L2 is carried out with metals
with at least three accessible coordination sites, for example,
with an octahedral or tetrahedral geometry, the most plausible
derivatives that could be obtained are those shown in Chart 3
Chart 3. Possible Species That Could Be Formed by
Reaction of Ligands L1 or L2 with Octahedral Metallic
Centers
(VI and VII), that is, dimeric or polymeric species. An interesting case of the formation of both type of derivatives in
silver complexes with bis(pyrazolyl)methane ligands with a
thioether function has been reported by Marchiò.22c In Chart 3
octahedral metallic centers have been drawn and species VII
has the three donor atoms in a facial disposition, although a
trans orientation of the pyridine fragment would also be possible
with respect to one of the pyrazole rings. For both structures, the
existence of bridging groups in the remaining positions could
give rise to the formation of species of higher nuclearity.
To assess the behavior of the ligands against metal centers
of different geometry, the reactions with Pd(II), Co(II), Ni(II),
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Scheme 2. Synthesis of the Palladium Complexes 1−6
Scheme 3. Synthesis and Structures of Complexes 7−12
Scheme 4. Synthesis and Structure of Complex 13
also blue and the presence of tetrahedral cobalt centers is also
proposed. Elemental analyses were performed on crystals that
were subjected to vacuum for about twelve hours and it was
found that the amount of solvent was lower than that in the
crystals used for X-ray diffraction. The lower solvent content in
these products was also confirmed by 1H NMR spectroscopy.
In the case of complex 10, thermogravimetric analysis was
performed on crystals not previously submitted to vacuum. In
the temperature range 30 to 110 °C a mass loss of 16% was
observed and this corresponds to 3 DMF molecules (per
dimer) assigned to the crystallization solvent. From 110 to
200 °C, another mass loss was observed up to a value of 28%.
This second loss should correspond to the two coordinated
DMF molecules per dimer. Endothermic peaks were observed
for each mass loss.
The reaction of L1 with silver(I) was also investigated. This
metallic center does not have stereochemical rigidity and this
could lead to new types of structures. When L1 was reacted
with AgPF6, crystals of 13 with the stoichiometry [Ag(PF2O2)(L1)]·1/2THF were obtained. The hydrolysis of hexafluorophosphate to give difluorophosphate is not uncommon, especially
in the presence of silver(I) centers,38 and this process can take
place with the water present in the AgPF6 solid used in the reaction. We were unable to obtain crystals of the hexafluorophosphate derivative. Complex 13 consists of box-like cyclic
dimers similar to those described previously, but in this case
they are connected through double difluorophosphate bridges
to give zigzag chains (see Scheme 4 and below for the solid
state structure).
1956
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Article
Table 1. Crystal Data and Structure Refinement for L2, 2·2Me2CO, 3, 4·Me2CO·0.5H2O, and 7·DMF
L2
empirical formula
fw
temp (K)
wavelength (Å)
cryst syst
space group
a (Å)
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
vol (Å3)
Z
density (calcd) (g/cm3)
abs coeff (mm−1)
F(000)
cryst size (mm3)
index ranges
reflns collected
independent reflns
Data/restraints/params
GOFc on F2
final R indices [I > 2σ(I)]
largest diff. peak and hole,
e·Å−3
2·2Me2CO
3
C16H19N5
281.36
230(2)
0.71073
monoclinic
P21/n
16.083(5)
9.929(3)
19.757(6)
C38H50Cl6N10O2Pd3
1210.78
230(2)
0.71073
monoclinic
P21/n
9.1235(9)
15.526(2)
17.465(2)
C36H43B3F12N10Pd3
1195.43
230(2)
0.71073
monoclinic
P21/c
11.949(3)
26.138(6)
16.170(3)
99.919(6)
99.508(3)
102.88(1)
3107.5(16)
8
1.203
0.076
1200
0.33 × 0.27 × 0.12
−19 ≤ h ≤ 19
−11 ≤ k ≤ 11
−23 ≤ l ≤ 23
16 747
5363 [R(int) = 0.1239]
5363/0/388
0.840
R1a = 0.0700
wR2b = 0.1615
0.187 and −0.197
2440.0(4)
2
1.648
1.465
1208
0.12 × 0.09 × 0.07
−11 ≤ h ≤ 9
−19 ≤ k ≤ 19
−20 ≤ l ≤ 21
16 892
4993 [R(int) = 0.0287]
4993/0/274
1.194
R1a = 0.0282
wR2b = 0.0812
0.712 and −0.741
4923.4(19)
4
1.613
1.166
2360
0.18 × 0.12 × 0.09
−14 ≤ h ≤ 14
−31 ≤ k ≤ 31
−19 ≤ l ≤ 19
37 068
8671 [R(int) = 0.0823]
8671/78/578
0.927
R1a = 0.0595
wR2b = 0.1556
1.185 and −0.949
4·Me2CO·0.5H2O
7·DMF
C47H66B3F12N10O1.50Pd3
1374.73
100(2)
0.71073
triclinic
P1̅
10.0566(4)
14.3393(5)
20.4904(5)
79.761(2)
89.847(2)
73.098(2)
2778.38(16)
2
1.643
1.047
1382
0.21 × 0.17 × 0.08
−12 ≤ h ≤ 12
−17 ≤ k ≤ 17
0 ≤ l ≤ 25
10 922
10922 [R(int) = 0.0000]
10922/2/713
1.054
R1a = 0.0331
wR2b = 0.0683
1.144 and −0.556
C39H57Cl6Co3N15O5
1205.49
230(2)
0.71073
triclinic
P1̅
12.1430(5)
12.9480(5)
21.0620(8)
88.990(2)
81.930(2)
81.516(2)
3242.8(2)
2
1.235
1.051
1238
0.21 × 0.15 × 0.09
−12 ≤ h ≤ 14
−15 ≤ k ≤ 15
−19 ≤ l ≤ 25
21 007
11286 [R(int) = 0.0341]
11286/0/617
0.831
R1a = 0.0487
wR2b = 0.1408
0.453 and −0.361
R1 = Σ||Fo| − |Fc|/Σ|Fo|. bwR2 = {Σw(Fo2 − Fc2)2/Σw(Fo2)2}1/2. cGOF = {Σ [w((Fo2 − Fc2)2)/(n-p)}1/2, where n = number of reflections and
p = total number of parameters refined.
a
Solid State Structure of L2. The spatial group is P21/n.
Symmetry elements are not present in the molecular structure
and, as expected, the pyrazole nitrogens are in an anti disposition
to avoid repulsion between the electron pairs (see Figure 1).
Two independent molecules are observed, which are connected
through two weak hydrogen bonds formed between Hα of one
molecule and the free nitrogen of one pyrazole ring of the other
molecule (dC27−N2 = 3.37 Å, dC11−N7 = 3.33 Å). These pyrazole
rings are also involved in a CH−π interaction between one
proton of the Me3 group and the pyridine ring of the other
molecule (dH4A−Ct = 3.08 Å, dH20C−Ct = 2.95 Å, Ct = centroid)
(see Figure 1).
These pairs of molecules interact to form chains through
weak CH−π interactions involving the pyrazole rings that
do not participate in the formation of the aforementioned
hydrogen bonds (dH7−Ct = 2.94 Å), and these chains run in a
parallel disposition through new CH−π interactions (dH5C−Ct =
3.06 Å) to complete the supramolecular structure.
Solid State Structure of the Complex [Pd 3Cl 6(bpz*m4py)2]·2Me2CO, 2·2Me2CO. Complex 2 is trinuclear
and presents an inversion center in the central Pd2 atom, a
situation that makes the two halves of the molecule identical
(Figure 2). The Pd2 atom is coordinated to two chloride
ligands and two nitrogens of the pyridine rings from the
bpz*m4py ligands, in a trans disposition, with a perfect square
planar geometry (τ4 = 0).41 The Pd1 centers, which are on both
sides of the molecule, adopt a slightly distorted square planar
The IR spectra of all complexes showed bands corresponding
to the stretching frequencies of the CN bonds typical of the
pyrazole and pyridine rings, as well as for the 2-Me-allyl group
and the BF4− (complexes 3-6) or difluorohosphate38d (complex
13, ν(P−F) and ν(P−O)) counteranions. The ν(B−F) of the
BF4− group bands were split, indicating a possible decrease in
the symmetry of the anions. Bands typical of free nitrate were
observed for 9−12. The presence of coordinated nitrate groups
was deduced for complexes 10, 11, and 12. Splitting of the
ν(NO) band that is of E′ symmetry in the free anion was
observed (two bands at around 1460 and 1295 cm−1 were
detected) and, in addition, the band of A1′ symmetry is now
active and appears at around 1030 cm−1.39 In complexes 10
and 11, the coordinated nitrate is bidentate, and we, therefore,
propose the same situation for 12.
As we have previously found for other complexes that
contain similar ligands,40 for a pair of derivatives with a specific
metallic fragment the derivative that contains ligand L2 (with
methylated pyrazolyl groups) is the most soluble.
Solid-State Characterization. The crystallographic information for L2, 2·2Me2CO, 3, 4·Me2CO·0.5H2O, 7·DMF,
9·2DMF, 10·3DMF, 11, and 13·0.5THF is given in Tables 1
and 2. Tables with a selection of bond lengths and angles are
gathered in the Supporting Information. A complete set of
parameters for the noncovalent interactions described below is
also given in the Supporting Information.
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Table 2. Crystal Data and Structure Refinement for 9·2DMF, 10·3DMF, 11, and 13·0.5THF
9·2DMF
empirical formula
fw
temp (K)
wavelength (Å)
cryst syst
space group
a (Å)
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
vol (Å3)
Z
density (calcd) (g/cm3)
abs coeff (mm−1)
F(000)
cryst size (mm3)
index ranges
reflns collected
independent reflns
data/restraints/params
GOFc on F2
final R indices [I > 2σ(I)]
largest diff. peak and hole, e·Å−3
C48H78N22Ni2O20
1400.74
230(2)
0.71073
monoclinic
P21/c
21.996(1)
12.9390(6)
25.184(1)
113.445(3)
6575.6(6)
4
1.415
0.658
2944
0.18 × 0.17 × 0.08
−27 ≤ h ≤ 27
−15 ≤ k ≤ 15
−31 ≤ l ≤ 31
44 241
13 332 [R(int) = 0.0952]
13332/0/845
0.932
R1a = 0.0664
wR2b = 0.1556
0.957 and −0.450
10·3DMF
C47H73N19Ni2O17
1293.62
230(2)
0.71073
triclinic
P1̅
10.133(1)
13.8385(6)
13.9286(6)
115.960(4)
95.722(5)
103.508(5)
1661.4(2)
1
1.293
0.641
680
0.19 × 0.16 × 0.12
−13 ≤ h ≤ 12
−18 ≤ k ≤ 18
−18 ≤ l ≤ 18
16 858
7912 [R(int) = 0.0347]
7912/0/416
1.101
R1a = 0.0689
wR2b = 0.2109
1.420 and −0.464
11
13·0.5THF
C30H36N16O14Zn2
975.49
230(2)
0.71073
monoclinic
C2/c
11.8548(6)
22.389(1)
19.3240(9)
C26H26Ag2F4N10O4.50P2
904.25
230(2)
0.71073
monoclinic
C2/c
24.466(2)
10.4265(7)
17.483(1)
103.487(3)
91.497(5)
4987.4(4)
4
1.299
1.031
2000
0.24 × 0.22 × 0.19
−13 ≤ h ≤ 14
−26 ≤ k ≤ 26
−21 ≤ l ≤ 22
14 172
4382 [R(int) = 0.0511]
4382/0/284
0.960
R1a = 0.0436
wR2b = 0.1098
0.481 and −0.343
4458.2(5)
4
1.347
1.005
1792
0.21 × 0.16 × 0.10
−27 ≤ h ≤ 28
−12 ≤ k ≤ 11
−20 ≤ l ≤ 20
11 750
3890 [R(int) = 0.0435]
3890/5/232
1.012
R1a = 0.0644
wR2b = 0.2005
1.158 and −0.529
R1 = Σ||Fo| − |Fc|/Σ|Fo|. bwR2 = {Σw(Fo2 − Fc2)2/Σw(Fo2)2}1/2. cGOF = {Σ [w((Fo2 − Fc2)2)/(n − p)}1/2, where n = number of reflections and
p = total number of parameters refined.
a
Figure 1. Two molecules of the ligand bpz*m4py, L2, connected by
hydrogen bonds (red) and CH−π interactions (purple).
Figure 2. X-ray structure of the complex [Pd3Cl6(bpz*m4py)2]·
2Me2CO, 2·2Me2CO. The pyrazolyl rings of other molecules are
indicated to show the CH−π interaction (purple). Hydrogen bonds
(red) and lone-pair−π interactions (brown) are also shown.
geometry (τ4 = 0.06). These palladium atoms are coordinated
to two chloride atoms and the two pyrazole rings of the ligand.
The Pd−N distances are in the range 2.02−2.04 Å. The ligand
bpz*m4py forms a six-membered metallacycle by coordination
to the Pd1 atoms and this ring adopts the typical boat conformation with the pyridine ring in the axial position, a common
arrangement for these types of ligands with one substituent in
the central carbon.16,17a,c,42 The dihedral angle PdNN/N4(pz)
is 140.69°, the bite angle of the chelate ligand is 85.28° and the
dihedral angle formed by the pyrazole rings is 107.44°. These
parameters, which are referred to as the structural parameters of
the ligand throughout this paper, were found to be structurally
related for the same type of derivative and a concomitant
increase or reduction in these three values was found.16b,17a,c,43
(A table in the Supporting Information contains all of these
parameters for the derivatives described in the paper whose
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structures were determined by X-ray diffraction). Comparison
of the data for complex 2 with those of other dichloropalladium
derivatives that contain bis(3,5-dimethylpyrazol-1-yl)methane
ligands bearing one substituent in the central carbon44 shows
that the values are similar except for the case of the pz−pz
angle, which is smaller for 2 (reported values are about 117°).
The two pyridine rings are nearly coplanar. Chlorine atoms
are not in the plane of the pyridine rings and the dihedral angle
between the coordination plane and the plane of the pyridine
rings is 42.87°.
The acetone molecules that crystallize in the structure (two
per trinuclear complex) establish different interactions with the
molecules; namely a lone pair−π interaction with a pyridine
ring, several hydrogen bonds and a CH−π interaction with a
pyrazole ring (Figure 2).
Molecules of the trinuclear complex interact on both sides
through weak hydrogen bonds between Cl1 of one molecule
and H4 of the pyrazole ring (H2) of a neighboring molecule
(dC2−Cl1 = 3.56 Å), thus leading to one-dimensional ribbons
running along the a-axis (see Figure 3). This structure can also
Figure 4. Formation of the 3D supramolecular structure for complex 2.
Projection along a axis. Pd···HC interactions are represented in green
and hydrogen bonds in red. Acetone molecules have been omitted for
clarity.
170°) and may be considered as a special type of hydrogen
bond. The nature of the anagostic interactions in d8 square
planar complexes was addressed theoretically and the conclusions were that the interaction is mainly electrostatic in nature
(partial covalence has been found only for the shortest distance
in the range) and there is no evidence for the involvement of
dz2 orbitals but rather dxz/yz in the interaction.46 The data for
complex 2 (dPd2···H7 = 2.79 Å and Pd−H−C angle of 147.80°)
unambiguously indicate that a double anagostic interaction is
present in each central palladium atom which, if these interactions
are considered, may be regarded as pseudo-octahedral. Different examples of anagostic interactions have been described in
palladium(II) chemistry that involve the approach of one,47
two48 or even more49 CH groups in a direction approximately
perpendicular to the coordination plane. However, these interactions usually take place with CH groups that belong to
ligands coordinated to the metal center. Our case is a rare
example of intermolecular anagostic interactions. It is possible
that these interactions exist in known structures but they have
not been found in cases where the 3D structure has not been
analyzed.
Solid State Characterization of the Complexes [Pd3(η3-C4H 7)3(bpzm4py)2](BF4)3 (3) and [Pd3(η 3-C4H 7) 3(bpz*m4py)2](BF4)3·Me2CO·0.5H2O (4·Me2CO·0.5H2O).
There are no symmetry elements in these complexes and therefore the three palladium atoms and the two ligands of the molecules are different. In the case of 3, some disorder exists for
the BF4− anions, the central allyl group and the pyrazolyl ring
that contain N12. Thus, the parameters or interactions involving these groups will not be detailed and neither the crystalline
structure.
All palladium atoms have a pseudo square planar geometry,
coordinated in all cases to a η3-allyl group and to the nitrogen
of the pyridine ring of both ligands (L1 or L2 for 3 and 4,
respectively) in the case of the central atom (Pd3) or to two
pyrazolyl rings of a specific ligand (terminal Pd atoms) (see
Figure 5 for complex 4). The metallacycles formed with these
atoms exhibit the usual boat conformation, with the pyridine
ring occupying the axial position, as is usual in these types of
Figure 3. Formation of the supramolecular ladder for complex 2
through hydrogen bonds (red). Acetone molecules have been omitted
for clarity.
be considered as a supramolecular ladder in which the rungs are
the “PdCl2(pyridine)2” units, the nodes are constituted by
the terminal palladium fragments and the sides of the ladder
are formed through the aforementioned hydrogen bonds. In
this ladder, however, the rungs are not perpendicular to the
sides.
Molecules of a specific ladder interact with four adjacent
ladders through two types of interaction: a hydrogen bond
between Cl2 and Me3pz (dCl2−C4 = 3.47 Å) and a Pd···H4Cpz
contact (see below) involving the central Pd atom (see Figure 4,
in which the ladders are represented perpendicular to the drawing
plane, bc plane). The angle formed between two adjacent ladders
is 65.8°. In this way, the supramolecular three-dimensional
framework of 2 is formed.
The Pd···HC interactions warrant specific comment. This
type of M···HC interaction can be described as agostic or
anagostic, with structural and spectroscopic differences45 between them (some confusion exists in the literature concerning
this differentiation). The former term implies shorter M···H
distances (1.8−2.3 Å) and small M−H−C angles (90−140°),
while the latter are characterized by relatively long M···H
distances (2.3−2.9 Å) and large M−H−C bond angles (∼110−
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Figure 6. Superposition plot of complexes 3 (pink) and 4 (blue). Pd3
atoms and Cα of one ligand, (C7 for 3 and C11 for 4), were used to
fit the two molecules. Palladium atoms are represented as balls and
hydrogen bonds are in red.
Figure 5. X-ray structure of the cation of complex 4, [Pd3(η3-C4H7)3(bpz*m4py)2]3+ including also one molecule of H2O, one molecule of
acetone and one BF4− anion. Intramolecular interactions are shown:
CH−π (purple), lone-pair−π (brown), anion−π (blue), and Pd···O
contact (green).
The orientation of the allyl groups in the terminal fragments
is the same as that found in similar derivatives,16 that is, with
the allylic methyl group pointing toward the α substituent
(pyridine in this case). The dihedral angles between the PdNN
plane and that of the allyl group range from 110.4 to 119.1°
in such a way that the C(central) to CH3 vector is pointing
away from the metal. In addition, in these fragments the allyl
methyl groups deviate more markedly from the allylic plane
(0.31−0.49 Å) than the central allyl methyl group (0.28 Å).
This deviation situates these methyl groups closer to the
pyridine ring.
An interesting aspect of complex 4 concerns the noncovalent
interactions. One pyridine ring exhibits, on one side, an anion−
π interaction involving a BF4− anion (dF3−Ct = 3.61 Å) along
with a CH−π interaction, on the other side, with the participation of an allylic methyl group (dH20A−Ct = 3.01 Å). The
other pyridine ring has a similar arrangement but differs in that
the interaction is not with an atom of an anion but with the
oxygen of a neutral molecule, the crystallization acetone; in other
words there is a lone-pair−π interaction (dO1−Ct = 3.60 Å) and a
CH−π interaction (dH44C−Ct = 3.11 Å) (see Figure 5). The
CH−π interactions may be the origin of the quoted values for
the dihedral angle between the allyl and the coordination planes
and the deviation of the allyl methyl groups in the terminal
fragments. In the context of these interactions, we reported a
theoretical study that demonstrated the synergy of anion−π
and CH−π interactions in triazine rings and this also included
examples in which the two interactions were present on
both sides of this heterocycle.30 Complex 4 can be considered
as another example that reflects this synergy in this case in a
pyridine ring.
In the case of complex 3, the CH−π interaction with the
participation of the allylic methyl groups is also present
according with the strong deviation of these groups from the
allylic plane.
There are also in both complexes CH−π interactions
involving the H3/H5 hydrogen atoms of the pyridine rings
and the nearest pyrazolyl groups. The H−Ct distances and the
C−H−Ct angles are in the range 2.7−3.1 Å and 111−122°,
respectively.
ligands.16,17a,c,42 Although these complexes are cationic, the
Pd−N distances are longer than those found in complex 2 (in
the range 2.07−2.12 Å). This is due to the higher trans influence of the allyl carbons in comparison to the chloride ligands.
In contrast to 2, in these cases, as expected, the cis coordination
of the two nitrogenated ligands in the central metallic atom is
forced by the presence of the η3-allyl group. The dihedral angles
of the pyridine rings with the Pd(3)NN plane are between
44.66° and 67.49°. A high steric hindrance would exist if the
two pyridine rings were coplanar. In the case of 4, the central
palladium atom exhibits an interaction with the oxygen from
the crystallization water that is approximately perpendicular to
the coordination plane and with the opposite orientation to
that of the allyl methyl group (Pd3···O2 = 3.005(1) Å).
The relative orientation of the three palladium fragments is
different in the two allyl complexes, as shown by the superposition of the two molecules (see Figure 6). In complex 3, the
two terminal groups are situated in an approximate syn disposition whereas in 4 the arrangement can be considered as anti.
Several possible factors could be responsible for this difference.
However, it is noteworthy that in 4 one BF4− anion is situated
between these two terminal metallic fragments and this participates in several hydrogen bonds involving, among other fragments, three methyl groups of the pyrazolyl rings. These groups
are not present in 3.
If the structural parameters of the nitrogenated ligands are
taken into account, it can be concluded that relatively similar
values are obtained for the two ligands of the complex in 3
while in the case of 4 there are significant differences. Values
between 149.0 and 157.6° were found for the PdNN/N4 angle
and the bite angle is in the range 86.7−89.8°; in both cases this
angle is comparable to those found in palladium complexes
with similar ligands.16b,43a As far as the dihedral angle between
pyrazole rings is concerned, values of 114.87° and 138.21° were
found for 4 and 135.34° for 3. The reported pz−pz angles are
around 124−125°.16
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Figure 7. Formation of the chains of cations in a head-to-tail disposition for complex 4 through double CH−π interactions (purple).
Figure 8. Structure of the box-like cyclic dimers of complexes 7 (a), 9 (b), 10 (c), 11(d), and 13 (e). Hydrogen atoms have been omitted for clarity.
In the case of 4, the packing of the molecules in the 3D
structure mainly involves the formation of hydrogen bonds
between the three types of BF4− anions and different protons of
the N-donor and allyl ligands as well as the acetone molecules and each particular F atom may participate in two or
more hydrogen bonds. The F3 atom that is involved in the
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Article
is in the range 86.5−89° for complexes that contain ligand L1
but is higher for derivative 10 (92.1°), which contains ligand L2
with methylated pyrazolyl groups. The dihedral angle between
the two pyrazolyl rings is in the range 137−143°, which is
higher than that found for the palladium complexes. However,
the most important difference between the derivatives with
square-planar or octahedral metallic centers is the MNN/N4
angle, which is in the range 141−154° in the former complexes
and 173−178° in the latter, which can be considered as exhibiting metallacycles with a half-chair disposition. The metal is very
close to the N4 plane (distances between 0.01 and 0.17 Å while for
complexes 2 and 4 this is in the range 0.64−0.95 Å). These
differences could be due to the steric requirements of the ligand
situated cis to the two pyrazolyl rings in the octahedral complexes.
In the case of the five-coordinate silver derivative, the bite
angle is the lowest of all the derivatives described here (80.63°)
and the other two parameters are more similar to those of
the palladium complexes (pz−pz angle =121.03°; MNN/N4
angle = 156.48°).
There are several intramolecular noncovalent interactions in
these box-like dimers that are common for the five derivatives
and may have an influence on their stability and shape. The two
pyridine rings are parallel and exhibit a π−π stacking interaction
(dCt···Ct = 3.32−3.55 Å for the octahedral complexes and 3.92 Å
for 13). This interaction should favor the orientation found
for these heterocycles. Besides, all the H atoms in this ring
are involved in weak interactions: H2 and H6 form hydrogen
bonds with oxygen (chloride or fluoride in the case of 7 and 13,
respectively) atoms of the ancillary ligands (X−C distances of
2.92−3.56 Å with one case of 3.90 Å) and H3 and H5 give rise
to CH−π interactions with the pyrazole rings of the same
ligand (dH−Ct = 2.60−3.00 Å). In some cases, the other side of
the pyrazole rings exhibits anion−π (range O−Ct = 2.76−
2.88 Å) interactions with nitrate anions. Some of these interactions are reflected in Figure 9, which corresponds to derivative 9.
See Supporting Information for more detailed data.
anion−π interaction also participates in the hydrogen bonding network. The same applies to the oxygen atom of the acetone
molecule.
A weak double CH−π interaction involving the pyrazole
rings coordinated to Pd2 and the allyl group of the Pd1 is also
observed (dH20C−Ct = 3.04 Å, dH19A−Ct = 3.14 Å) and this gives
rise to the formation of chains, as shown in Figure 7.
X-ray Structures of Complexes 7·DMF, 9·2DMF, 10·3DMF,
11, and 13·0.5THF. The molecular structures of complexes
7·DMF, 9·2DMF, 10·3DMF and 11 are quite similar and consist
of box-like cyclic dimers formed by the self-assembly of two metal
centers and two ligands in a head-to-tail disposition (L1 in 7, 9
and 11 and L2 in 10, see Figure 8a−d). In the case of 13·0.5THF
also similar dinuclear species are formed involving L1 (Figure 8e)
but in this case they are connected through double PF2O2−
bridges to give zigzag chains (see below).The structures of
these molecular box-like dimers will be explained together.
In the case of 7, two types of units that are very similar exist
with Co(1) and Co(2) atoms. Except in the case of 9, an inversion center exists and this means that only one-half of the
structure is unique. In all complexes except 13, the metal
ions exhibit a distorted octahedral geometry with the three
nitrogens (two from the pyrazolyl rings of one ligand and
the third from the pyridine ring of the second ligand) in a
facial disposition. The other three positions are completed
with different ligands: a chloride and two DMF molecules
in the case of 7 (one DMF trans to py), three DMF molecules
for 9 and a bidentate nitrate and a DMF molecule for 10 and
11. In the case of 11 one oxygen of the nitrate group is trans to
the pyridine ring while in 10 this position is occupied by the
DMF molecule, possibly because steric repulsion would exist
between this molecule and the methyl groups of the pyrazole
rings if they were in a relative cis disposition (Figure 8). The
counteranions are [CoCl4]2− in the case of 7 and nitrate for the
rest of the derivatives. This octahedral geometry is in contrast
to that reported by Carrano et al. for similar species formed with the
(4-carboxyphenyl)bis(3,5-dimethylpyrazolyl)methane ligand
and the M(II) centers Zn,20 Cu,21 Co, and Ni,20,21 where lower
coordination numbers were found.
In the case of 13, the silver centers are five-coordinate, being
bonded to two difluorophosphate groups and to three nitrogen
atoms of two ligands that are arranged in a similar disposition to
the previous cyclic dimers [see Figure 8e]. The ideal values for τ5
for a trigonal bipyramid or a square planar pyramid are 1 and 0,
respectively. The value found for the silver center in 13 is 0.33,
reflecting a rather distorted square planar pyramidal geometry.50
The M−N distances differ from one metal to the other (in
the range 2.14−2.17 Å for Co, 2.04−2.07 Å for Ni and Zn
and 2.27−2.42 Å for Ag). In general, there are no significant
differences between the bonds with pyrazole or pyridine rings
for a given metal except for 13 where shorter bonds are found
with pyridine, the more basic heterocycle. In all cases, the
two M−N(pyrazole) bonds are different in length. The Ag−O
bonds are in the range 2.55−2.68 Å while for the derivatives
with octahedral metallic centers, the M−O distances are shorter.
They are in the range 2.03−2.16 Å with the exception of one
Zn−O(nitrate) bond in the case of 11 (2.35 Å), a complex in
which an asymmetric nitrate is present. The nitrate group of 10
is bonded in a symmetric way. The bite angle of the coordinate
nitrate group is 60.41° in the case of 10 but is smaller in 11
(56.71°).
As far as the nitrogenated ligands are concerned, in the case
of the derivatives with octahedral metallic centers the bite angle
Figure 9. Noncovalent interactions present in the dinuclear unit of
complex 9. Hydrogen bonds (red), π−π stacking (black), anion−π
(blue) and CH−π (purple) interactions are shown. The ancillary
ligands and their interactions have been omitted for clarity.
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Figure 10. Complex 7. Chains arranged along the b-axis formed through the interaction of the box-like cyclic dimers of Co(1) (a) or Co(2) (b).
In (a) the direct hydrogen bonds have been omitted. The red circle in b represents the region where the apolar methyl groups are gathered.
The lower value of the MNN/N4 angle found for the silver
derivative in comparison with the octahedral derivatives has
consequences for two parameters of the box-like dimers: (i) the
metal−metal distances are in the range 7.1−7.6 Å for the
octahedral derivatives while the value for 13 is 6.48 Å and (ii)
the angle β of the π−π stacking interaction (i.e., the angle
formed by the H−Ct and the H−plane lines) is 25.6° for 13
but is in the range 6.1−10.7° for the octahedral derivatives.
This implies that the pyridine rings are offset to a greater extent
in the silver complex.
In the following paragraphs a description of the crystal
structures of the different derivatives will be given separately.
To facilitate the discussion and concerning the box-like cyclic
dimers we will mention the long and short side of the box
referring to the lines M−pyridine−M and M−Cα, respectively.
Complex [CoCl(bpzm4py)(DMF) 2 ] 2 (CoCl 4 )·DMF,
7·DMF. The dimers that contain Co(1) atoms are arranged
along the b-axis and this contacts the short side of the box
through weak and double hydrogen bonds of the type A−HC/
CH−A, where A = O1A of a DMF molecule and CH = C5H5
(position 4 of a pyrazole ring). These interactions are complemented by hydrogen bonds established between the two dimers
with a [CoCl4]2− ion that acts as a bridge connecting them. The
dimers that contain Co(2) are also arranged along the b-axis, in
this case facing the long side of the box and with an interaction
taking place only through hydrogen bonds with a [CoCl4]2−
ion that also acts as a bridge (all [CoCl4]2− ions are equivalent)
(Figure 10). The apolar methyl groups of one DMF molecule (cis
to pyridine) of each dimer are situated in the same region of space,
probably due to hydrophobic contacts (see circle in Figure 10b).
The interaction of the two types of chains to give the supramolecular structure takes place through direct hydrogen bonds
(MeDMF with Cl) or through the participation of [CoCl4]2−
or noncoordinated DMF molecules that act as bridges (see
Figure 11).
Figure 11. X-ray structure of 7·DMF along the a-axis. The different
chains are highlighted.
Complex [Ni(bpzm4py)(DMF)3]2(NO3)4·2DMF, 9·2DMF.
The supramolecular three-dimensional framework of 9 consists
of chains of dimers that extend along the b-axis in a very similar
fashion to that found for the Co(2) dimers of complex 7. The
interaction between two consecutive dimers takes place
through hydrogen bonds with nitrate groups or with aggregates
of nitrate/noncoordinated DMF molecules that act as bridges
(Figure 12). In this case the apolar groups of coordinated DMF
molecules are also arranged nearby in space but in this case the
arrangement involves the two DMF molecules that are cis to
the pyridine group. See circle in Figure 12.
The aforementioned chains give rise to sheets in the bc plane
with different hydrogen bonds involving nitrate and noncoordinated
DMF molecules. The formation of hydrogen bonds with nitrate
and crystallization solvent molecules also allows the interaction of
the sheets to generate the 3D structure.
Complex [Ni(NO3)(bpz*m4py)(DMF)]2(NO3)2·3DMF,
10·3DMF. The supramolecular framework of 10, in which
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bonding interaction involving the noncoordinated nitrate
groups (all these anions are equivalent) that act as bridges.
It is interesting to note that the pyridine heterocycles in this
complex exhibit interactions on both sides of the ring, π−π
stacking on one side and anion−π interactions on the other, a
fact that could reflect the synergy of these interactions, as
described previously.29f,51
The three-dimensional framework is formed by the
interactions between different chains through hydrogen bonds
involving nitrate and DMF groups. Thus, when viewed along
the a-axis and considering the position of the metallic centers, a
honeycomb disposition is found in which channels containing
the DMF molecules are formed (see Figure 14).
Complex [Zn(NO3)(bpzm4py)(DMF)]2(NO3)2, 11. In this
derivative the dimers are also aligned through the longer side of
the box to form a chain that extends along the [101] direction.
However, in this case, the consecutive dimers are not perfectly
parallel and, in fact, two types of alternating orientations are
present (see Figure 15). The dihedral angle between the pyridine rings of two consecutive dimers is 21.61°. The contact of
two consecutive units takes place through three types of interaction. In the center of the chain, one of the noncoordinated
nitrate anions (containing O11) establishes two anion−π interactions with two pyridine rings, one for each dimer (dO11−Ct =
3.38). In this way, this derivative can also be considered as
another example of synergy between π−π stacking and anion−
π interactions.29f,51 The other oxygen atoms of this nitrate form
hydrogen bonds with the Hα atom of both dimers. In the
section of the chain in which the dimers are closest or farthest
apart, hydrogen bonds are established either directly between
the two units or with nitrate groups acting as bridges.
As in other previous examples, the nitrate and DMF molecules give rise to a complex system of hydrogen bonds to form
the supramolecular three-dimensional framework. If the structure is viewed in the (101) plane, a honeycomb disposition of
the chains is observed with channels that extend along the
[101] direction in a similar way to that found in complex 10.
If we consider the supramolecular structure of the octahedral
complexes that contain box-like cyclic dimers, it can be concluded that the most common mode of interaction between
dimers to form chains arises from the face of the long side of
the box and involves interactions through direct hydrogen
bonds between the dimers or with the intermediacy of nitrate
or free DMF molecules as bridges. In some cases, anion−π
interactions between nitrate anions and the pyridine rings
were also found. The 3D structure is formed through a complex
system of hydrogen bonds. In two derivatives a honeycomb
disposition of the metallic centers was found.
Figure 12. Complex 9. Interaction of the boxes through hydrogen
bonds to form chains that extend along the b-axis. The red circle
represents the region where the apolar methyl groups are gathered.
the nitrate anions play an important role, can also be viewed by
considering the formation of chains with the aforementioned
dimers connected along the a-axis through the long sides of the
box, as found in 9 and dimers of Co2 in 7. However, in this
case the interaction between contiguous dimers involves more
than hydrogen bonds. As it can be seen in Figure 13, a double
Figure 13. Complex 10. Interaction of the box-like dimers through
anion−π interactions (blue) and hydrogen bonds (red) to give chains
that extend along the a-axis.
head-to-tail anion−π interaction involving pyridine rings and
the terminal oxygen atoms (O3) of the coordinated nitrate
groups is established (dO3−Ct = 3.60 Å). These oxygen atoms
also participate in the formation of hydrogen bonds with different H atoms of the N-donor ligand. The interaction between
the dimers is complemented with a more peripheral hydrogen-
Figure 14. View along the a-axis of the 3D supramolecular structure for complex 10. (a) Dimers and anions in black with the crystallization DMF
molecules in gray. (b) Framework with space-filling representation of the dimers and anions.
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Figure 15. Complex 11. Hydrogen bonds (red) and anion−π interactions (blue) between box-like dimers to form a chain that extends the [101]
direction. The interactions are only shown for two dimers.
Complex [Ag(μ2-κ2-O,O-PF2O2)(L1)]2·0.5THF, 13·0.5THF.
The box-like dimers of 13 are bonded through double difluorophosphate bridges to generate zigzag chains that extend along
the b-axis. These chains are connected through noncovalent interactions to give rise to sheets in the bc plane (see Figure 16).
Figure 17. THF molecules, in spacefill, situated between the sheets in
complex 13·0.5THF.
some cases 1H, 19F{1H}, 31P{1H} and 13C{1H} NMR spectra
were recorded in order to obtain information about the structures of the new complexes in solution.
In the mass spectra of derivatives 1 and 2 the highest mass
peak corresponds to trinuclear species, more specifically to the
cations [Pd3Cl4L2]+ for 1 and [Pd3Cl5L2]+ for 2. This indicates
that the complexes remain trinuclear in solution, at least to
some extent. Peaks corresponding to dinuclear or mononuclear
species were also observed. In the case of the allyl complexes 3
and 4, polynuclear species were not detected and the peaks of
higher intensity were those corresponding to [Pd(Me-allyl)L]+.
The absence of polynuclear species, in contrast to the situation
found for the chloride derivatives, may be due to the higher
trans influence of the allyl groups than the chloride ligands, a
characteristic that makes the Pd−N bonds weaker in complexes
3 and 4. Peaks corresponding to the same mononuclear species
were observed for 5 and 6.
In complexes 7−12, at least one of the complexes synthesized with each metal exhibits peaks corresponding to a dinuclear species. For the cobalt derivatives, for example, the
peaks [Co2Cl2(L1)2]2+ for 7 and [Co2(py-CH2-pz*)2]+ for 8
are observed. For the Zn complexes, only fragments containing
one metallic atom are observed for 11 while for 12 the species
[Zn2(L2) + 5H2O]+ gives rise to the most intense peak. In the
case of 13, peaks corresponding to the box-like cyclic dimer
with one or two difluorophosphate groups are observed. For
all the peaks described, the calculated isotope pattern was in
agreement with the formulation.
Figure 16. Four chains of complex 13 that form a sheet in the bc
plane. Hydrogen bonds (red), π−π stacking interactions (black) are
shown in a region of the plane.
These interactions are of two types: (i) Hydrogen bonds that
are present in the four corners of the boxes. In two corners the
oxygen or fluorine atoms of the difluorophosphate groups act as
hydrogen acceptors and in the other two the CHα group and
other CH groups of the pyrazolyl rings act as hydrogen donors.
(ii) A π−π stacking interaction involving a pyridine and a pyrazolyl ring of dimers of adjacent chains. Considering that both
pyridine rings of a particular unit are involved in this interaction, a kind of short column with π−π stacking involving four
rings is formed (see Figure 16). The crystallization THF molecules are situated between the sheets as shown in Figure 17.
When considering the different noncovalent interactions
found in the complexes described in this paper it is noteworthy
that several possible examples of synergy between some of
these interactions have been found: more specifically, between
anion−π interactions and π−π stacking and also between hydrogen bonds and anion−π interactions where the π ring acts
as hydrogen donor.
In the crystalline structures of the different species described
here the “pyrazolyl embrace” described by Reger28a was not found.
This phenomenon involves a concerted set of intermolecular
CH−π and π−π stacking interactions that associate the four
pyrazolyl rings from two nearby bpzm sites.
Solution Chemistry. ESI-TOF or MALDI-TOF mass spectra
(see Experimental Section part for details), UV−vis and, in
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fragments (1.59 for 3 and 1.36 ppm for 4) whereas the signals
of the central allyl group appear in the usual range for these
groups: 2.23 and 2.24 ppm, for 3 and 4, respectively. This difference must be due to the effect of the ring current anisotropy
of the pyridine ring if the allyl group has the orientation shown
in Chart 4 (CH−π interaction), as found in the solid state. This
The UV−vis spectra of ligands L1 and L2 and those of
complexes 1−12 were recorded at room temperature in methanol at concentrations in the range 10−4 to 10−5 M. L1 and L2
exhibit absorption bands at around 220 and 260 nm and these
are assigned to π−π* Intra-Ligand Charge Transfer (ILCT)
transitions corresponding to the pyrazole and to the pyridine
moieties, respectively. The molar extinction coefficient (ε) is
around five times higher for the former absorption. These
regions fit with the maximum absorption bands in the spectra
of N-methypyrazole52 or N-methyl-3,5-dimethylpyrazole53 and
4-methylpyridine.54 For ligand L1 an additional absorption at
308 nm (very low intensity) is observed but this does not
appear for ligand L2. However, this absorption is present not
only for several complexes with ligand L1 but also for complexes with ligand L2. The ILCT(py) absorption with small
energy changes appears in the absorption spectra. However, the
corresponding ILCT(pz) absorption is not observed in the
spectra of the complexes. Similar behavior has been ascribed in
other cases to the coordination of the ligands in solution.55,13h
The red-shift of the ILCT(py) absorption in Pd complexes
1−6 is significant, as is the appearance of two bands at 334
and 466 nm for complex 2, which could be assigned to metalto-ligand charge transfer (MLCT) absorptions. These bands
reflect the coordination of the ligand in the Pd complexes in
solution. In the Co(II) complexes 7 and 8 and in the Ni complex 9, bands at around 310 nm can be assigned to the ILCT
absorptions56 but MLCT absorptions were not observed.
In contrast, in the Ni(II) complex 10 an additional band at
388 nm can be assigned to an MLCT absorption.57 Solvent
dependence of the energy of this MLCT band is observed as
this band is blue-shifted by 9 nm in MeCN. This fact can be
considered to be indicative of ligand coordination.58 Additionally, in the Co(II) complexes 7 and 8 a weak absorption is
observed at around 520 nm due to d-d transitions of a d7 high
spin complex. Similarly, in the Ni(II) complexes these weak
absorptions appear in the region 550−630 nm, with two bands
evident in the case of complex 9. In the Zn(II) complexes 11
and 12, although the ILCT band at around 300 nm can be
observed, an MLCT band does not appear in the spectra.
The NMR spectra provide information in the cases of
complexes 3−6, 11, 12, and 13. As mentioned previously, the
chloride derivatives 1 and 2 are very insoluble in the most
common solvents and the 1H NMR spectra were registered in
dmso-d6, giving rise to complex spectra with broad resonances.
Broad and multiple resonances were also observed in the 1H
NMR spectra of the paramagnetic complexes 7−10. The signal
assignment was made considering bibliographic information
and taking into account the data of 1H−1H COSY, 1H−13C
g-HMQC, g-HMBC, and NOE difference spectra.
The 1H NMR spectra (acetone-d6) of the trinuclear allylic
derivatives 3 and 4 are very informative. The presence of a
unique and symmetric nitrogenated ligand along with two types
of symmetric η3-allylic groups in a 1:2 ratio was deduced. The
same conclusion was drawn from the 13C{1H} NMR data. The
ratio of the two allyl groups is consistent with the presence
of the trinuclear species in solution. In mononuclear 2-Meallyl-palladium complexes with α-substituted bis(pyrazolyl)methane
ligands one usually observes evidence for the two isomers that
differ in the orientation of the allyl group, albeit in different
ratios.16 In 3 and 4, the spectra reflect that only one orientation
of the allyl groups is present in each terminal palladium fragment. In relation with this orientation, it is worth noting the
low chemical shift of the methyl group of the terminal allyl
Chart 4. NOEs Observed for Complex 4 (Indicated with
Arrows)
orientation has been found to be more stable in allyl derivatives
with similar ligands.16 The NOEs observed between the Me3
hydrogens of complex 4 and the Hsyn and Hanti protons of
the allyl group also confirm the allyl orientation (see Chart 4).
An NOE effect is also observed between Hα and H5/Me5 of the
pyrazolyl rings, indicating that the pyridine moiety is situated in
the axial position of the metallacycle (see Chart 4).
Comparison of the signals of the nitrogenated ligands with
those of the free ligands shows deshielding of the pyrazole
resonances, which is consistent with coordination to the metal
center. However, in the case of the pyridine signals only a very
small deshielding is observed for the H2/H6 protons but shielding is evident for the H3/H5 hydrogen atoms (shift of about
0.5 ppm), an effect that must be due to the influence of the π
cloud of the pyrazole rings and is consistent with the CH−π
interaction detected in the solid state (see Figure 5).
If the structures of derivatives 3 and 4 are considered and the
asymmetry introduced by the central allyl group is taken into
account, the following groups should appear as different in
the 1H and 13C{1H} NMR spectra: (i) the two halves of the
terminal allyl groups; (ii) the two pyrazolyl rings of a ligand,
and (iii) the two halves of the pyridine rings. However, at
room temperature all these groups as observed as symmetric. A
process of apparent allyl rotation of the central allyl group
would create this symmetry. However, this process has only
been observed for similar systems above room temperature,16,59
and we propose that this is not operating in our case. If the
pyridine rings exhibit unrestricted rotation, the H2/H6 and
H3/H5 pyridine protons would be isochronous and we propose
that as the explanation for point iii but points i and ii should be
yet operating. The equivalence observed in the allyl and pyrazolyl groups could be due to the fact that they are situated
far away from the central allyl group. In any case, a variable
temperature 1H NMR experiment was carried out for the two
derivatives (down to −80 °C). The only splitting was observed
in the case of 4. For this derivative, two resonances for the Hsyn
of the terminal groups were detected from −40 °C and below.
This may be due to the fact that these protons are situated nearer
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ing resonance of the Hα proton was observed with the expected
relative integration and this remained unchanged with time.
However, at 0 °C the intensity of this signal started to decrease
in such a way that after 42 min, the intensity of the resonance
was 37% of the initial signal. We propose that deuteration of
this position takes place and, as a consequence, the deuterium
coupled signal (JCD = 22 Hz) was detected in the corresponding 13C{1H} NMR spectrum. In the case of the silver derivative
13, we also observed the progressive disappearance of the Hα
resonance at room temperature in methanol-d4. We consider
that this selective deuteration is an interesting process and we
will investigate this phenomenon in future work.
the central group than the others and at low temperature, with
less thermal motion, they are observed as different.
The 1H and 13C NMR spectra of the mononuclear complexes
5 and 6 reflect the presence of a unique isomer with a ligand
containing two equivalent pyrazolyl groups thus supporting the
coordination of the two pyrazolyl rings to the palladium atom.
The 1H NMR resonances of the allyl fragment are similar to the
terminal allyl groups of 3 and 4 indicating a similar orientation
of this group with respect the N-donor ligand.
The 1H NMR spectrum of 11 was recorded in methanol-d4
because the complex was not soluble in acetone and in DMSO
total ligand decoordination would be expected. The room
temperature spectrum reflects the presence of the corresponding free ligand, indicating that a dissociation process occurs in
solution. The Hα resonance was not observed, a fact that will
be explained below. To analyze the possible presence of the
box-like structures at low temperature, variable temperature
1
H NMR spectra were registered in methanol-d4. When the
temperature was decreased, a new species was observed at
−50 °C and this was more clearly observed at −90 °C. A 1H−
1
H COSY experiment was performed in order to assign the new
signals. A deshielding of 0.4−0.6 ppm was found for the pyrazolyl resonances with respect to those in the free ligand − an
observation in accordance with coordination of these rings to a
metal center. Interestingly, shielding is found for the pyridine
signals. In the case of H2/H6(py) resonance the shift to higher
field was 0.45 ppm but the marked change (0.95 ppm) in the
case of H3/H5(py) is noteworthy. We propose that the decrease
in the temperature slows down the decoordination process and
that the new species detected at −90 °C is the box-like dimer,
in which the π−π stacking between the two pyridine rings and
the CH−π interaction of the H3/H5 atoms with the pyrazolyl
rings observed in the solid state are maintained in solution and
are responsible for the observed anomalous pyridine chemical
shifts. Considering that the box-like unit has two ligands, the
amount of box-like dimer detected at −90 °C is around 20%.
In the case of 12 at room temperature, besides broad signals
of the free ligand, a new set of ligand resonances was detected
in the 1H NMR spectrum in methanol-d4. The shift to higher or
lower field was in the same sense as observed for the box-like
unit of complex 11 (albeit with lower absolute values) and thus
we propose that the resonances are due to the dimer unit that is
detected in this complex at room temperature. The interchange
process with the ligand must occur at a lower rate than in the
case of 11. The relative amount of box-like unit detected at
this temperature is 38%. This difference between the two Zn
derivatives is in accordance with the data from the mass spectra.
In the silver complex 13, the 1H and 13C NMR spectra reflect
the presence of a unique and symmetric nitrogenated ligand
with chemical shifts different from those of the free ligand. A
similar spectrum is observed at low temperature (−80 °C). In
the proton resonances a deshielding or shielding is observed for
the pyrazolyl or pyridyl protons, respectively. This is similar to
that found for the box-like units in the Zn derivatives, a fact that
points to the existence of the dimer unit in solution and with an
influence of the π−π stacking and the CH−π interaction in the
pyridyl signals. The expected resonances for the PF2O2− group
are observed in the corresponding 19F and 31P NMR
spectra.38a,c
As stated previously, in the case of 11 a resonance for Hα was
not observed. This signal was observed for 12 and, as a result,
we monitored by 1H NMR a freshly prepared methanol-d4
solution of 11 at −50 °C. At this temperature the correspond-
■
CONCLUSIONS
Two new all nitrogen donor ditopic ligands that can act as
tridentate systems, bis(pyrazol-1-yl)(pyridine-4-yl)methane (L1)
and bis(3,5-dimethylpyrazol-1-yl)(pyridine-4-yl)methane (L2),
have been synthesized. The reaction of these ligands with
metallic centers yields different derivatives whose structure
depends mainly on the metal geometry. With square-planar
ions such as Pd(II) the preferential formation of trinuclear
species is observed with the central atom bonded to two
pyridine rings and the terminal centers interacting with the two
pyrazolyl rings in a chelate fashion. The other two positions are
completed with two chloride ligands or one allyl ligand. In the
case of the allyl derivatives the use of an excess of the nitrogenated ligands allows the formation of mononuclear complexes. Neither of these reactions leads to the formation of
species with an uncoordinated bis(pyrazolyl) chelate group.
When the reaction of L1 or L2 is performed with metal
centers that are able to give an octahedral geometry (M =
Co(II), Ni(II), Zn(II)), box-like cyclic dimers are formed by
self-assembly of two metal centers and two ligands in a head-totail disposition. All metal ions exhibited a distorted octahedral
geometry with the three nitrogens, two from the pyrazolyl rings
of one ligand, and the third from the pyridine ring of the other,
in a facial disposition. DMF molecules or nitrate anions complete
the coordination sphere of the metal. In the solid state, the
dimers exhibit different noncovalent interactions including an
internal π−π stacking between the two pyridine rings. The
dinuclear units are aligned to form chains that in the majority
of cases face the long side of the box and interact through
hydrogen bonds and, in some cases, also through anion−π
interactions involving pyridine rings.
Relatively similar box-like units are formed in a fivecoordinate silver complex, but in this case they are bonded
through double difluorophosphate bridges to give chains. Noncovalent interactions between the chains give rise to the formation of sheets.
The structural characteristics of the nitrogenated ligands in the
palladium and silver complexes are relatively similar and differ
from those of the derivatives with octahedral metallic centers.
The different noncovalent interactions found in the molecular structures apparently influence the shape of the molecules.
In some derivatives possible examples of synergy between noncovalent interactions have been found: for example, between
anion−π interactions and π−π stacking in pyridine rings and
also between hydrogen bonds and anion−π interactions where
the π ring acts as a hydrogen donor.
In the study of the solution chemistry, evidence for polynuclear fragments was deduced from the mass spectra and NMR
information. A clear effect of the noncovalent interactions on the
NMR chemical shifts of some resonances was observed.
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2009, 38, 1400−1417. (k) Kim, M.; Boissonnault, J. A.; Dau, P. V.;
Cohen, S. M. Angew. Chem., Int. Ed. 2011, 50, 1−5.
(5) Yaghi, O. M.; Li, H.; Groy, T. L. Inorg. Chem. 1997, 36, 4292−4293.
(6) (a) Alvaro, M.; Carbonell, E.; Ferrer, B.; Llabrés i Xamera, F. X.;
García, H. Chem.Eur. J. 2007, 13, 5106−5112. (b) Llabrés i Xamera,
F. X.; Corma, A.; García, H. J. Phys. Chem. 2007, 111, 80−85.
(7) Wuerthner, F.; You, C.; Saha-Moeller, C.; Chantu, R. Chem. Soc.
Rev. 2004, 33, 133−146.
(8) (a) Caneschi, A.; Gatteschi, D.; Lalioti, N.; Sengregorio, C.
Angew. Chem., Int. Ed. 2001, 40, 1760−1763. (b) Clerac, R.; Miyasaka,
H.; Yamashita, M.; Coulon, C. J. Am. Chem. Soc. 2002, 124, 12837−
12844. (c) Ichikawa, S.; Kimura, S.; Mori, H.; Yoshida, G.; Tajima, H.
Inorg. Chem. 2006, 45, 7575−7577. (d) Meihaus, K. R.; Rinehart, J. D.;
Long, J. R. Inorg. Chem. 2011, 50, 8484−8489.
(9) (a) Olenyuk, B.; Fechtenkötter, A.; Stang, P. J. J. Chem. Soc.,
Dalton Trans. 1998, 1707−1728. (b) Stang, P. J. Chem.Eur. J. 1998,
4, 19−27. (c) Fujita, M.; Umemoto, K.; Yoshizawa, M.; Fujita, N.;
Kusukawa, T.; Biradha, K. Chem. Commun. 2001, 509−518.
(d) Papaefstathiou, G. S.; MacGillivray, L. R. Coord. Chem. Rev.
2003, 246, 169−196. (e) Ward, M. D. Annu. Rep. Prog. Chem. Sect. A
2001, 97, 293−392.
(10) (a) Jeffrey, G. A. An Introduction to Hydrogen Bonding; Oxford
University Press: New York, 1997. (b) Beatty, A. M. Coord. Chem. Rev.
2003, 246, 131−143. (c) Awaleh, M. O.; Badia, A.; Brisse, F. Cryst.
Growth Des. 2005, 5, 1897−1906. (d) Subramanian, S.; Zaworotko,
M. J. Coord. Chem. Rev. 1994, 137, 357−401.
(11) (a) Janiak, C. Dalton Trans. 2000, 3885−3896 and references
therein. (b) Ponzini, F.; Zagha, R.; Hardcastle, K.; Siegel, J. S. Angew.
Chem., Int. Ed. 2000, 39, 2323−2325. (c) Kim, J. L.; Nikolov, D. B.;
Burley, S. K. Nature 1993, 365, 520−527. (d) Kim, Y.; Geiger, J. H.;
Hahn, S.; Sigler, P. B. Nature 1993, 365, 512−520. (e) Salonen, L. M.;
Ellermann, M.; Diederich, F. Angew. Chem., Int. Ed. 2011, 50, 4808−
4842.
(12) Lenthall, J. T.; Steed, J. W. Coord. Chem. Rev. 2007, 251, 1747−
1760.
(13) (a) Schottel, B. L.; Chifotides, H. T.; Dunbar, K. R. Chem. Soc.
Rev. 2008, 37, 68−83. (b) Mascal, M.; Armstrong, A.; Bartberger, M.
J. Am. Chem. Soc. 2002, 124, 6274−6276. (c) De Hoog, P.; Gamez, P.;
Mutikainen, I.; Turpeinen, U.; Reedijk, J. Angew. Chem., Int. Ed. 2004,
43, 5815−5817. (d) Alkorta, I.; Rozas, I.; Elguero, J. J. Am. Chem. Soc.
2002, 124, 8593−8598. (e) Quiñonero, D.; Garau, C.; Rotger, C.;
Frontera, A.; Ballester, P.; Costa, A.; Deyá, P. M. Angew. Chem., Int. Ed.
2002, 41, 3389−3392. (f) Berryman, O. B.; Bryantsev, V. S.; Stay,
D. P.; Johnson, D. W.; Hay, B. P. J. Am. Chem. Soc. 2007, 129, 48−58.
(g) Mooibroek, T. J.; Black, C. A.; Gamez, P.; Reedijk, J. Cryst. Growth
Des. 2008, 8, 1082−1093. (h) Manzano, B. R.; Jalón, F. A.; Ortiz,
I. M.; Soriano, M. L.; Gómez de la Torre, F.; Elguero, J.; Maestro,
M. A.; Mereiter, K.; Claridge, T. D. V. Inorg. Chem. 2008, 47, 413−
428. (i) Gamez, P.; Mooibroek, T. J.; Teat, S. J.; Reedijk, J. Acc. Chem.
Res. 2007, 40, 435−444. (j) Robertazzi, A.; Krull, F.; Knapp, E.-W.;
Gamez, P. CrystEngComm. 2011, 13, 3293−3300.
(14) (a) Nishio, M. Cryst. Eng. Commun. 2004, 6, 130−158.
(b) Braga, D.; Grepioni, F.; Tedesco, E. Organometallics 1998, 17,
2669−2672. (b) Bogdanovic, G. A.; Spasojevic-de-Biré, A.; Zaric, S. D.
Eur. J. Inorg. Chem. 2002, 1599−1602. (c) Fujii, A.; Shibasaki, K.;
Kazama, T.; Itaya, R.; Mikami, N.; Tsuzuki, S. Phys. Chem. Chem. Phys.
2008, 10, 2836−2843. (d) Tsuzuki, S.; Fujii, A. Phys. Chem. Chem.
Phys. 2008, 10, 2584−2954.
(15) (a) Steel, P. J. Acc. Chem. Res. 2005, 38, 243−250. (b) Eddaoudi,
M.; Moler, D. B.; Li, H.; Chen, B.; Reineke, T. M.; O’Keefe, M.; Yagi,
O. M. Acc. Chem. Res. 2001, 34, 319−330. (c) Blake, A. J.; Champness,
N. R.; Hubberstey, P.; Li, W.-S.; Withersby, M. A.; Schröder, M. Coord.
Chem. Rev. 1999, 183, 117−138. (d) Rosseinsky, M. J. Microporous
Mesoporous Mater. 2004, 73, 15−30. (e) Ma, B.-Q.; Mulfort, K. L.;
Hupp, J. T. Inorg. Chem. 2005, 44, 4912−4914. (f) Felloni, M.; Blake,
A. J.; Hubberstey, P.; Wilson, C.; Schröder, M. Cryst. Growth Des.
2009, 9, 4685−4699. (g) Yang, W.; Lin, X.; Blake, A. J.; Wilson, C.;
Hubberstey, P.; Champness, N. R.; Schröder, M. Inorg. Chem. 2009,
48, 11067−11078.
The Zn and Ag complexes with L1 also exhibit an unexpected selective deuteration in position α of the nitrogenated
ligand in methanol-d4 solution.
The mononuclear allyl-Pd derivatives have noncoordinated
nitrogen atoms and the metal centers in the complexes with
box-like cyclic units contain ligands that can be easily displaced.
Thus, these derivatives could be used as building units to form
MOF structures. This aspect will also be studied in future work.
■
ASSOCIATED CONTENT
S Supporting Information
*
X-ray crystallographic files in CIF format. ORTEP representations
of the structures. Description of the synthesis and characterization of
the new derivatives. Tables with structural parameters of the ligands
and data for noncovalent interactions. This material is available
free of charge via the Internet at http://pubs.acs.org.
■
AUTHOR INFORMATION
Corresponding Author
*E-mail: [email protected].
Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS
This work was supported by the MICINN of Spain
(CTQ2011-24434, FEDER Funds) and the Junta de
Comunidades de Castilla-La Mancha-FEDER Funds (PCI080054 and PEII11-0214). We thank the MEC of Spain for a FPU
grant (GD) and INCRECYT program (contract to MCC).
■
DEDICATION
This paper is dedicated to the memory of our wonderful
colleague, Prof. Purificación Escribano, who dedicated her life
to chemistry and to defend the rights of women.
■
REFERENCES
(1) (a) Holliday, B. J.; Mirkin, C. A. Angew. Chem., Int. Ed. 2001, 40,
2022−2043. (b) Moulton, B.; Zaworotko, M. J. Chem. Rev. 2001, 101,
1629−1658. (c) Seidel, S. R.; Stang, P. J. Acc. Chem. Rev. 2002, 35,
972−983. (d) Leong, W. L.; Vittal, J. J. Chem. Rev. 2011, 111, 688−
764.
(2) Rowsell, J. L. C.; Yaghi, O. M. Microporous Mesoporous Mater.
2004, 73, 3−14.
(3) Corma, A.; García, H.; Llabrés i Xamena, F. X. Chem. Rev. 2010,
110, 4606−4655.
(4) (a) Ferey, G.; Mellot-Draznieks, C.; Serre, C.; Millange, F.;
Dutour, J.; Surble, S.; Margiolaki, I. Science 2005, 309, 2040−2042.
(b) Rowsell, J. L. C.; Yaghi, O. M. Angew. Chem., Int. Ed. 2005, 44,
4670−4679. (c) Rosi, N. L.; Eckert, J.; Eddaoudi, M.; Vodak, D. T.;
Kim, J.; O’Keeffe, M.; Yaghi, O. M. Science 2003, 300, 1127−1129.
(d) Latroche, M.; Surble, S.; Serre, C.; Mellot-Draznieks, C.;
Llewellyn, P. L.; Lee, J. H.; Chang, J. S.; Jhung, S. H.; Ferey, G.
Angew. Chem., Int. Ed. 2006, 45, 8227−8231. (e) Kitagawa, S.; Kitaura,
R.; Noro, S. Angew. Chem., Int. Ed. 2004, 43, 2334−2375. (f) Kuppler,
R. J.; Timmons, D. J.; Fang, Q.-R.; Li, J.-R.; Makal, T. A.; Young,
M. D.; Yuan, D.; Zhao, D.; Zhuang, W.; Zhou, H.-C. Coord. Chem. Rev.
2009, 253, 3042−3066. (g) Krishna, R.; Long, J. R. J. Phys. Chem. C.
2011, 115, 12941−12950. (h) Galli, S.; Masciocchi, N.; Colombo, V.;
Maspero, A.; Palmisano, G.; López-Garzón, F. J.; Domingo-García, M.;
Fernández-Morales, I.; Barea, E.; Navarro, J. A. R. Chem. Mater. 2010,
22, 1664−1672. (i) Barea, E.; Tagliabue, G.; Wang, W.-G.; PérezMendoza, M. J.; Mendez-Liñan, L.; López-Garzón, F. J.; Galli, S.;
Masciocchi, N.; Navarro, J. A. R. Chem.Eur. J. 2010, 16, 931−937.
(j) Perry, J. J. IV; Perman, J. A.; Zaworotko, M. J. Coord. Chem. Rev.
1968
dx.doi.org/10.1021/cg201677s | Cryst. Growth Des. 2012, 12, 1952−1969
Crystal Growth & Design
Article
(36) Sluis, P. vd.; Spek, A. L. Acta Crystallogr., Sect. A 1990, A46,
194−201.
(37) (a) Tan, R.-Y.; Hong, J.; Du, M.; Tang, L.-F. J. Organomet.
Chem. 2007, 692, 1708−1715. (b) Otero, A.; Fernández-Baeza, J.;
Antiñolo, A.; Lara-Sánchez, A.; Martínez-Caballero, Emilia; Tejeda, J.;
Sánchez-Barba, L. F.; Alonso-Moreno, C.; López-Solera, I. Organometallics 2008, 27, 976−983.
(38) (a) Fernández-Galán, R.; Manzano, B. R.; Otero, A.; Lanfranchi, M.;
Pellinghelli, M. A. Inorg. Chem. 1994, 33, 2309−2312. (b) Brooks,
N. R.; Blake, A. J.; Champness, N. R.; Cunningham, J. W.; Hubberstey, P.;
Schröder, M. Cryst. Growth Des. 2001, 1, 395−399. (c) Albrecht, M.;
Hübler, K.; Kaim, W. Z. Anorg. Allg. Chem. 2000, 626, 1033−1037.
(d) Bruno, G.; Lo Schiavo, S.; Piraino, P.; Faraone, F. Organometallics
1985, 4, 1098−1100.
(39) Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coordination Compounds; John Wiley & Sons: New York, 1986, pp 124, 256.
(40) Elguero, J.; Guerrero, A.; Gómez de la Torre, F.; de la Hoz, A.;
Jalón, F. A.; Manzano, B. R.; Rodríguez, A. M. New J. Chem. 2001, 25,
1050−1060.
(41) Yang, L.; Powell, D. R.; Houser, R. P. Dalton Trans. 2007, 955−964.
(42) Byers, P. K.; Canty, A. J.; Honeyman, R. T. J. Organomet. Chem.
1990, 385, 417−427.
(43) (a) Carrión, M. C.; Jalón, F. A.; López-Solera, I.; Manzano,
B. R.; Sepúlveda, F.; Santos, L.; Rodríguez, A. M.; Moreno, M.;
Martinez-Ripoll, M. Can. J. Chem. 2005, 83, 2106−2119. (b) Tsuji, S.;
Swenson, D. C.; Jordan, R. F. Organometallics 1999, 18, 4758−4764.
(44) Sánchez-Méndez, A.; de Jesús, E.; Flores, J. C.; Gómez-Sal, P.
Inorg. Chem. 2007, 46, 4793−4795.
(45) Brookhart, M.; Green, M. L. H.; Parkin, G. Proc. Natl. Acad. Sci.
2007, 104, 6908−6914.
(46) Zhang, Y.; Lewis, J. C.; Bergman, R. G.; Ellman, J. A.; Oldfield, E.
Organometallics 2006, 25, 3515−3519.
(47) Singh, N.; Singh, B.; Thapliyal, K.; Drew, M. G. B. Inorg. Chim.
Acta 2010, 363, 3589−3596.
(48) (a) Huynh, H. V.; Han, Y.; Ho, J. H. H.; Tan, G. K. Organometallics 2006, 25, 3267−3274. (b) Feng, Y. L.; Liu, S. X. Chin. J.
Chem. 2002, 20, 841−845.
(49) Baker, A. T.; Crass, J. K.; Maniska, M.; Craig, D. C. Inorg. Chim.
Acta 1995, 230, 225−229.
(50) Addison, A. W.; Rao, T. N.; Reedijk, J.; van Rijn, J.; Verschoor,
G. C. J. Chem. Soc., Dalton Trans. 1984, 1349−1356.
(51) Alkorta, I.; Blanco, F.; Deyá, P. M.; Elguero, J.; Estarellas, C.;
Frontera, A.; Quiñonero, D. Theor. Chem. Acc. 2010, 126, 1−14.
(52) Wakamatsu, S.; Barltrop, J. A.; Day, A. C. Chem. Lett. 1982,
667−670.
(53) Sucrow, W.; Bredthauer, G. Chem. Ber. 1983, 116, 1520−1524.
(54) Anwar; Duan, X.-M.; Komatsu, K.; Okada, S.; Matsuda, H.;
Oikawa, H.; Nakanishi, H. Chem. Lett. 1997, 247−248.
(55) Ortiz, M. I.; Soriano, M. L.; Carranza, M. P.; Jalón, F. A.; Steed,
J. W.; Mereiter, K.; Rodríguez, A. M.; Quiñonero, D.; Deyà, P. M.;
Manzano, B. R. Inorg. Chem. 2010, 49, 8828−8847.
(56) Roy, A. S.; Biswas, M. K.; Weyhermüller, M.; Ghosh, P. Inorg.
Chim. Acta 2010, 363, 2874−2880.
(57) (a) Carrasco, R.; Cano, J.; Ottenwaelder, X.; Aukauloo, A.;
Journaux., Y.; Ruiz-García, R. Dalton Trans. 2005, 2527−2538.
(b) Ottenwaelder, X.; Aukauloo, A.; Journaux, Y.; Carrasco, R.;
Cano, J.; Cervera, B.; Castro, I.; Curreli, S.; Muñoz, M. C.; Roselló,
A. L.; Soto, B.; Ruiz-García, R. Dalton Trans. 2005, 2516−2526.
(c) Trujillo, A.; Fuentealba, M.; Carrillo, D.; Manzur, C.; Ledoux-Rak,
I.; Hamon, J.-R.; Saillard, J.-Y. Inorg. Chem. 2010, 49, 2750−2764.
(58) (a) Lever, A. B. P. Inorg. Chem. 1990, 29, 1271−1285. (b) Curtis,
J. C.; Sullivan, B. P.; Meyer, T. J. Inorg. Chem. 1983, 22, 224−236.
(59) (a) Guerrero, A.; Jalón, F. A.; Manzano, B. R.; Rodríguez, A.;
Claramunt, R. M.; Cornago, P.; Milata, V.; Elguero, J. Eur. J. Inorg.
Chem. 2004, 549−556. (b) Jalón, F. A.; Manzano, B. R.; Moreno-Lara, B.
Eur. J. Inorg. Chem. 2005, 100−109.
(16) (a) Arroyo, N.; Gómez-de la Torre, F.; Jalón, F. A.; Manzano,
B. R.; Moreno-Lara, B.; Rodríguez, A. M. J. Organomet. Chem. 2000,
603, 174−184. (b) Carrión, M. C.; Díaz, A.; Guerrero, A.; Jalón, F. A.;
Manzano, B. R.; Rodríguez, A.; Paul, R. L.; Jeffery, J. C. J. Organomet.
Chem. 2002, 650, 210−222.
(17) (a) Carrión, M. C.; Díaz, A.; Guerrero, A.; Jalón, F.; Manzano,
B.; Rodríguez, A. M. New J. Chem. 2002, 26, 305−312. (b) Caballero,
A.; Carrión, M. C.; Espino, G.; Jalón, F. A.; Manzano, B. R. Polyhedron
2004, 23, 361−371. (c) Carrión, M. C.; Jalón, F. A.; Manzano, B. R.;
Rodríguez, A. M.; Sepúlveda, F.; Maestro, M. Eur. J. Inorg. Chem. 2007,
3961−3973. (d) Carrión, M. C.; Sepúlveda, F.; Jalón, F. A.; Manzano,
B. R.; Rodríguez, A. M. Organometallics 2009, 28, 3822−3833.
(18) (a) Trofimenko, S. Scorpionates: the Coordination Chemistry
of Polypyrazolylborate Ligands; Imperial College Press: London, 1999.
(b) Otero, A.; Fernández-Baeza, J.; Antiñolo, A.; Tejeda, J.; LaraSánchez, A. Dalton Trans. 2004, 1499−1510.
(19) Santillan, G. A.; Carrano, C. J. Inorg. Chem. 2007, 46, 1751−1759.
(20) Santillan, G. A.; Carrano, C. J. Dalton Trans. 2008, 3995−4005.
(21) Santillan, G. A.; Carrano, C. J. Inorg. Chem. 2008, 47, 930−939.
(22) (a) Liu, C.-S.; Guo, L.-Q.; Ma, S.-T.; Hu, M. Acta Crystallogr. 2008,
C64, m308−m310. (b) Liu, C.-S.; Chen, P.-Q.; Yang, E.-C.; Tian, J.-L.; Bu,
X.-H.; Li, Z.-M.; Sun, H.-W.; Lin, Z. Inorg. Chem. 2006, 45, 5812−5821.
(c) Bassanetti, I.; Marchiò, L. Inorg. Chem. 2011, 50, 10786−10797.
(23) Wang, J.-J.; Zhou, J.-N.; Liu, C.-S.; Shi, X.-S.; Chang, Z.; Yan,
L.-F.; Bu, X.-H.; Ribas, J. J. Mol. Struct. 2008, 875, 160−166.
(24) Calhorda, M. J.; Costa, P. J.; Crespo, O.; Gimeno, M. C.; Jones,
P. G.; Laguna, A.; Naranjo, M.; Quintal, S.; Shi, Y.-J.; Villacampa,
M. D. Dalton Trans. 2006, 4104−4113.
(25) Ward., M. D.; McCleverty, J. A.; Jeffery, J. C. Coord. Chem. Rev.
2001, 222, 251−272.
(26) Reger, D. L.; Watson, R. P.; Smith, M. D.; Pellechia, P. J.
Organometallics 2005, 24, 1544−1555.
(27) Reger, D. L.; Semeniuc, R. F.; Pettinari, C.; Luna-Giles, F.;
Smith, M. D. Cryst. Growth Des. 2006, 6, 1068−1070.
(28) (a) Reger, D. L.; Watson, R. P.; Smith, M. D. Inorg. Chem. 2006,
45, 10077−10087. (b) Reger, D. L.; Gardinier, J. R.; Semeniuc, R. F.;
Smith, M. D. Dalton Trans. 2003, 1712−1718. (c) Reger, D. L.; Semeniuc,
R. F.; Little, Ch. A.; Smith, M. D. Inorg. Chem. 2006, 45, 7758−7769.
(29) (a) Reddy, A. S.; Vijay, D.; Sastry, G. M.; Sastry, G. N. J. Phys.
Chem. B 2006, 110, 2479−2481. (b) Reddy, A. S.; Vijay, D.; Sastry,
G. M.; Sastry, G. N. J. Phys. Chem. B 2006, 110, 10206−10207.
(c) Escudero, D.; Frontera, A.; Quiñonero, D.; Deyà, P. M. Chem.
Phys. Lett. 2008, 456, 257−261. (d) Vijay, D.; Zipse, H.; Sastry, G. N
J. Phys. Chem. B 2008, 112, 8863−8867. (e) Garcia-Raso, A.; Alberti,
F. M.; Fiol, J. J.; Tasada, A.; Barceló-Oliver, M.; Molins, E.; Escudero,
D.; Frontera, A.; Quiñonero, D.; Deyà, P. M. Inorg. Chem. 2007, 46,
10724−10735. (f) Frontera, A.; Quiñonero, D.; Costa, A.; Ballester, P.;
Deyà, P. M. New J. Chem. 2007, 31, 556−560. (g) Quiñonero, D.;
Frontera, A.; Garau, C.; Ballester, P.; Costa, A.; Deyà, P. M. Chem. Phys.
Chem. 2006, 7, 2487−2491. (h) Zaccheddu, M.; Filippi, C.; Buda, F. J.
Phys. Chem. A 2008, 112, 1627−1632. (i) Quiñonero, D.; Frontera, A.;
Escudero, D.; Costa, A.; Ballester, P.; Deyà, P. M. Theor. Chem. Acc.
2008, 120, 385−393. (j) Mignon, P.; Loverix, S.; De Proft, F.; Geerlings,
P. J. Phys. Chem. A 2004, 108, 6038−6044. (k) Escudero, D.; Frontera,
A.; Quiñonero, D.; Deyà, P. M. J. Comput. Chem. 2009, 30, 75−82.
(30) Quiñonero, D.; Deyà, P. M.; Carranza, M. P.; Rodríguez, A. M.;
Jalón, F. A.; Manzano., B. R. Dalton Trans. 2010, 39, 794−806.
(31) Kharasch, M. S.; Sailer, R. C.; Mayo, F. R. J. Am. Chem. Soc.
1938, 60, 882−884.
(32) (a) Dent, W. T.; Long, R.; Wilkinson, G. J. Chem. Soc. 1964,
1585−1588. (b) Tatsuno, Y.; Yoshida, T.; Seiotsuha. Inorg. Synth.
1979, 19, 220−223.
(33) SAINT+ v7.12a. Area-Detector Integration Program; BrukerNonius AXS. Madison: Wisconsin, USA, 2004.
(34) Sheldrick, G. M. SADABS version 2004/1. A Program for
Empirical Absorption Correction; University of Göttingen: Göttingen,
Germany, 2004.
(35) SHELXTL-NT version 6.12. Structure Determination Package;
Bruker-Nonius AXS: Madison, Wisconsin, USA, 2001.
1969
dx.doi.org/10.1021/cg201677s | Cryst. Growth Des. 2012, 12, 1952−1969