Download 1 - SUrface

1
1. Introduction
The capacity of steric saturation of metal centers through secondary
interactions, such as M-C interactions, has been recently demonstrated by a
series of mono- and heterobimetallic compounds based on the 2,6-diphenylphenol
(HOdpp) ligand.1-6 In these complexes, extensive metal-C interactions support
the low metal coordination numbers. In an effort to further analyze the role of
metal-C interactions in heavy s-block metal complexes we here report on the
structural characterization of two K-Odpp compounds where secondary
interactions have been identified as the structure determining principle. The
strong tendency for potassium metal to form -interactions demonstrates itself by
comparing the co-ligand-free [K(Odpp)]∞, 1, with the aqua complex
{[K2(Odpp)2H2O]2}∞, 2, that not only displays a significantly different
coordination behavior, but also a significantly reduced degree of K-C
interactions, due to K-OH2 coordination and agostic interactions.
2. Experimental
2.1 Materials and Methods
All reactions were performed using modified Schlenk techniques under an
inert gas atmosphere. 2,6-diphenylphenol (HOdpp) was purchased and dried
under vacuum for 3 h. 1,3,5-tri-tert-butylbenzene (Mes*H) was prepared
2
according to literature procedures.7 Commercially available alkali metal hydrides
(stored under mineral oil) were washed three times with hexane, dried, and stored
in a drybox. Anhydrous tetrahydrofuran (THF) and toluene were obtained
utilizing the VAC atmospheres DRI-SOLV solvent system and degassed using
three freeze/thaw cycles. Compounds 1 and 2 were isolated from reaction
mixtures containing either Na and K aryloxides (1), or Li and K aryloxides (2), as
described in detail below. Lithium aryloxide was obtained as described, but the
sodium and potassium metal aryloxides (AOdpp, A = Li, Na, K) were prepared
using modified literature procedures,6 by refluxing the metals in toluene in the
presence of 2,6-diphenylphenol. Deprotonation of the ligand was monitored by
IR spectroscopy.
Single crystal X-ray diffraction experiments were performed on 1 and 2
where the crystals were removed from the Schlenk tube under a stream of Ar and
immediately covered with a layer of viscous hydrocarbon oil (Paratone N, Exxon).
A suitable crystal was selected under the microscope, attached to a glass fiber,
and immediately placed in the low-temperature nitrogen stream of the
diffractometer.8 All data sets were collected using a Siemens SMART system,
complete with 3-circle goniomenter and CCD detector. The data sets were
collected by using graphite monochromated Mo Kα radiation (λ = 0.71073 Å).
The data collections nominally covered a hemisphere of reciprocal space utilizing
a combination of three sets of exposures, each with a different φ angle, and each
exposure covering 0.3° in ω. Crystal decay was monitored by repeating the initial
frames at the end of the data collection and analyzing the duplicate reflections. In
3
both cases, no decay was observed. An absorption correction was applied
utilizing the program SADABS.9 The crystal structures of all compounds were
solved by Direct Methods, as included in the SHELXTL program package.10 The
structures were refined by full-matrix least-squares refinement on F2 (SHELX93).10 All hydrogen atoms except those on H2O were placed geometrically and
refined by using a riding model. Hydrogen atoms of the water molecules in
compound 2, were located on the difference map and freely refined. Thermal
parameters for hydrogen atoms were refined with Uiso constrained at 1.2 (for nonmethyl groups) times Ueq of the carrier C atom. Scattering factors were those
provided with the SHELX program system.10
CCDC 740755 (1) and 740756 (2) contains the supplementary
crystallographic data for this paper. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
2.2 General Synthetic Procedure
Carius tubes were charged with a mixture of two alkali metal alkoxides
inside a drybox along with the flux agent Mes*H, then sealed under reduced
pressure (< 40 mtorr). The tubes were heated in an oven maintaining a
temperature of 200° C, followed by cooling to room temperature. Crude crystals
were of insufficient quality for single crystal X-ray analysis, therefore products
were worked up as indicated below. The crude products were transferred into a
4
Schlenk flask and washed with hexane (2 x 15 mL) to remove Mes*H and
recrystallized as indicated. Crystals were removed from the flask for X-ray
diffraction under positive Ar pressure. For both compounds yields were low, as
only a few crystals were obtained that were utilized for single crystal x-ray
analysis. Furthermore, the isolated crystals were obtained from a solution that
likely contained multiple products.
Synthesis of [K(Odpp)]∞, 1.
[Na(Odpp)] (2 mmol, 0.54 g), [K(Odpp)] (2 mmol, 0.57 g), and Mes*H
(2.0 mmol, 0.5 g) were heated in a sealed Carius tube to 200°C for 13 days. The
crude product was insoluble in toluene (50 mL), even when heated to 100°C
(using a hot oil bath). The solution was cooled to 60°C and THF (8 mL) was
slowly added until the mixture dissolved. The solution was filtered through a
Celite-padded frit, yielding a clear, dark green solution that was concentrated to
initiate crystal formation. Crystallization occurred after 5 days in a 5°C
refrigerator, with crystals as colorless blocks.
Synthesis of {[K2(Odpp)2H2O]2}∞, 2.
[Li(Odpp)] (2 mmol, 0.50 g), [K(Odpp)] (2 mmol, 0.57 g), and Mes*H
(2.0 mmol, 0.5 g) were heated to 200°C for 13 days. The bulk product was
insoluble in toluene (40 mL), even when heated to 100°C (using a hot oil bath).
The solution was cooled to 60°C, whereupon THF (3 mL total) was slowly added
to the mixture until the crude product dissolved. The solution was filtered
5
through a Celite-padded frit, yielding a clear, light purple/pink solution that was
concentrated to initiate crystal formation. Crystallization occurred after 5 days in
a 5°C refrigerator, with crystals as colorless rods.
3 Results and Discussion
3.1 Synthesis
In an attempt to prepare heterobimetallic Na/K (1) or Li/K (2) Odpp
complexes, two different, previously prepared aryloxides were heated in the
presence of a flux agent. This route had been used successfully to prepare
aryloxide based heterobimetallic species containing combinations of alkalialkaline earth metals,1-3 two different alkaline earth metals,3 and alkali-lanthanide
metal combinations.3,4,11
In an attempt to expand this work to combinations of two alkali metals,
identical reaction conditions were utilized to those used previously.1-3 In analogy
to prior work, a distinct sensitivity towards solvents was detected; the use of polar
THF has previously resulted in the isolation of homometallic species.2 In contrast,
crystallization from pure toluene afforded the heterobimetallic target compounds;
however, the insolubility of the target compounds in toluene alone led to the use
of THF – and the dissociation of the heterobimetallic species into the
homometallic counterparts. The amount of THF needed to solubilize the products
likely led to the dissociation of the potentially formed heterobimetallic species.
6
Despite crystallization from THF/toluene mixtures neither of the reaction
products contains coordinated THF molecules, indicating that extensive K-C
coordination maybe advantageous over a small number of K-THF interaction. A
similar phenomenon was recently observed with [Ba(6-Ph)2B(Ph)2(thf)3][BPh4],
where 6 Ba-C coordination was favored over Ba-THF coordination.12
Theoretical studies indicate that the sum of the weaker Ba-C interactions
provided an energetic advantage over a smaller number of Ba-THF interactions.
In an attempt to prepare heterobimetallic Na/K (1) or Li/K (2) Odpp complexes,
two different, previously prepared aryloxides were heated in the presence of a
flux agent. This route had been used successfully to prepare aryloxide based
heterobimetallic species containing combinations of alkali-alkaline earth metals,13
two different alkaline earth metals,3 and alkali-lanthanide metal
combinations.3,4,11
In an attempt to expand this work to combinations of two alkali metals,
identical reaction conditions were utilized to those used previously.1-3 In analogy
to prior work, a distinct sensitivity towards solvents was detected; the use of polar
THF has previously resulted in the isolation of homometallic species.2 In contrast,
crystallization from pure toluene afforded the heterobimetallic target compounds;
however, the insolubility of the target compounds in toluene alone led to the use
of THF – and the dissociation of the heterobimetallic species into the
homometallic counterparts. The amount of THF needed to solubilize the products
likely led to the dissociation of the potentially formed heterobimetallic species.
7
Despite crystallization from THF/toluene mixtures neither of the reaction
products contains coordinated THF molecules, indicating that extensive K-C
coordination maybe advantageous over a small number of K-THF interaction. A
similar phenomenon was recently observed with [Ba(6-Ph)2B(Ph)2(thf)3][BPh4],
where 6 Ba-C coordination was favored over Ba-THF coordination.12
Theoretical studies indicate that the sum of the weaker Ba-C interactions
provided an energetic advantage over a smaller number of Ba-THF interactions.
This phenomenon is less prevalent for smaller metals, as they are not capable of
this larger number of metal-C interactions, and thus a preference of THF
coordination over -interactions is observed. The similar size of K+ (1.37 Å, CN
6) and Ba+2 (1.35 Å, CN 6)13 provide the platform for this comparison.
The aqua complex 2 is the result of the unintentional introduction of water
into the solution. Water introduction was likely the result of the multiple
manipulations made attempting to dissolve the insoluble material.
3.2 Structural Chemistry
Complexes 1 and 2 crystallize as 1-D coordination polymers. Compound
1 consists of an infinite ladder structure with additional K-C interactions,
whereas 2 consists of discrete K2(OR)2(OH2)2 polyhedra that aggregate into an
infinite structure via K-C interactions. The significant structural differences in 2
result from potassium-water coordination and K-H agostic interactions that are
absent in 1.
8
3.2.1 Crystal Structure of [K(Odpp)]∞, 1
Compound 1 crystallizes in the monoclinic space group P21/c, with one
potassium atom and one aryloxide ligand present in the asymmetric unit. Details
in regards to the crystal data collection and refinement are summarized in Table 1,
with selected bond lengths and angles provided in Table 2. Figure 1 illustrates an
overall view of 1, with a more detailed image of the K-C bonding given in
Figure 2.
Table 1. Crystal Data and Structure Refinement Details for [K(Odpp)]∞, 1, and
{[K2(Odpp)2H2O]2}∞, 2.
formula
FW
T [K]
crystal system
space group
a [Å]
b [Å]
c [Å]
β [°]
V [Å3]
Z
ρcalcd [Mg m-3]
μ [mm-1]
measured reflections
unique reflections [I > 2σ(I)]
parameters
R [I > 2σ(I)]
wR2 (all data)
GooF
1
C18H13KO
284.38
101(2)
Monoclinic
P2(1)/c
5.5909(7)
20.699(2)
11.664(2)
96.761(2)
1340.5(3)
4
2
C36H28K2O3
586.78
97(2)
Monoclinic
P2(1)/c
9.737(2)
13.465(2)
21.676(4)
98.445(3)
2811.2(8)
4
1.409
0.387
8687
3320 [R(int) = 0.0454]
181
R1 = 0.0547, wR2 =
0.1208
R1 = 0.0775, wR2 =
0.1402
1.079
1.386
0.374
27883
6966 [R(int) = 0.0757]
378
R1 = 0.0631, wR2 = 0.1234
R1 = 0.0973, wR2 = 0.1377
1.052
9
[K(Odpp)]∞ displays a polymeric structure; with puckered K2O2
rhombohedra propagating to form a 1-D ladder (see Figure 1). The potassium
atoms obtain a formal coordination number of three to neighboring oxygen atoms.
Interestingly, the K-O (rung) distances are significantly shorter [2.566(2) Å] than
the K-O (strand) distances that compose the 1-D propagation [2.804(2) and
2.852(2) Å]. The internal angles of the repeating K2O2 units sum to 360°, thus
confirming the planar geometry of this repeating group. The low formal
coordination number of three requires the large potassium center to form
extensive K-C interactions. A typical cutoff for these interactions is 3.5 Å,1,5 as
such each potassium is involved in nine -interactions (see Figure 2); five in a
2:3 bonding mode from one ligand and four (2:2) from the next one in the
chain, with an average K-C distance of 3.02 Å.
The propensity for metal-C interactions is also evident in the rubidium
congener [Rb(Odpp)]∞,6 which is isostructural to 1. The only significant
difference results from the larger size of Rb and that the Rb complex has ten RbCinteractions instead of nine. A further indication into the propensity for K-C
interactions comes from {K6(6,3-oBP)2(3-oBP)4(py)4}∞ (oBP = o-tertbutylphenoxide; py = pyridine),14 where despite K-N coordination eight 2 type
intramolecular K-C interactions are observed. Furthermore, individual
hexameric subunits link via two 6 intermolecular K-C contacts.
10
Figure 1. An illustration of [KOdpp]∞, 1, showing the K-O repeating ladder motif.
Dashed lines indicate select K∙∙∙π interactions (see Figure 2 for all K∙∙∙π
interactions) and continuation of the ladder chain. For clarity, the ladder fragment
is emphasized where only one Odpp ligand is depicted, but additional Odpp
ligands are represented by their oxygen atoms. Hydrogen atoms are omitted for
clarity, carbon atoms are shown as spheres, and all other atoms are shown as
ellipsoids at 30% probability.
11
Figure 2. An illustration of [KOdpp]∞, 1. Dashed lines indicate K∙∙∙π interactions.
Further repeating units are removed to illustrate the π saturation of the metal
center. Hydrogen atoms are omitted for clarity, carbon atoms are shown as
spheres, and all other atoms are shown as ellipsoids at 30% probability.
Table 2. Selected bond distances (Å) and bond angles (°) for [K(Odpp)]∞, 1.
K(1)-O(1)
2.566(2)
K(1)-O(1A)
2.804(2)
K(1)-O(1B)
2.852(2)
K(1)-C(1B)
K(1)-C(2)
K(1)-C(7)
K(1)-C(8)
K(1)-C(12)
3.404(2)
3.470(2)
2.993(2)
3.290(2)
3.240(2)
K(1)-C(1A)
K(1)-C(6)
K(1)-C(13)
K(1)-C(14)
O(1)-K(1)-O(1A)
O(1)-K(1)-O(1B)
O(1A)-K(1)-O(1B)
96.08(5)
97.25(5)
162.56(7)
K(1)-O(1)-K(1A)
K(1)-O(1)-K(1B)
K(1A)-O(1)-K(1B)
83.92(5)
82.75(5)
162.56(7)
Symmetry transformations used to generate equivalent atoms:
A: -x+1,-y+1,-z+2
B: -x,-y+1,-z+2
C: x-1,y,z
3.125(2)
3.186(2)
3.041(2)
3.464(3)
12
Remarkably, no K-THF contacts are observed despite the crystallization of
1 from a solution containing THF. While an individual K-C interaction is
weaker than a K-THF contact, the sum of all K-C interactions appears to
compete in strength with the stronger but fewer K-O(donor) contacts. This
assertion gains support by the K-C energies calculated by Dougherty et al.,
where significantly large values have been reported (K-C 19 kcal/mol vs. KOH2, 18 kcal/mol).15 The strength of the K-OH2 interaction maybe similar in
strength to that of K-THF, as both water and THF have similar dipole moments
(H2O, 1.85 D; THF, 1.75 D).16
3.2.2 Crystal structure of {[K2(Odpp)2H2O]2}∞, 2
Compound 2 crystallizes in the monoclinic space group P21/c with two
potassium centers, two aryloxide ligands and one water molecule within the
asymmetric unit. The polyhedron reveals a center of symmetry located in the
center of the K4OR4(OH2)2 core. Pertinent crystallographic data are summarized
in Table 1, while selected bond lengths and angles are tabulated in Table 3.
Figure 3 shows a detailed view of the tetrameric core, while Figures 4 and 5
provide extended views of the aggregation pattern with secondary interactions
included.
13
Figure 3. A representation of {[K2(Odpp)2H2O]2}∞, 2, showing only the K4O6
core. All atoms are shown as ellipsoids at 30% probability. O(3) and O(3A) are
contributed from the bridged water molecules, while O(1)/O(1A) and O(2)/O(2A)
are contributed from the Odpp ligands.
14
Figure 4. A side view of the polymeric chain. Extensive K∙∙∙π interactions are
observed within the K4O6 subunit as well as K∙∙∙π interactions linking between the
K4O6 subunits. The dashed lines indicate K∙∙∙π interactions. Hydrogen atoms are
ommited for clarity, carbon atoms are shown as spheres and all other atoms are
shown as ellipsoids at 30% probability.
15
Figure 5. Illustration of the K-H interactions present within one of the K4O6
subunits of 2. Dashed lines represent K∙∙∙H agostic interactions. All noninteraction hydrogen atoms were omitted for clarity, carbon atoms are shown as
spheres, and all other atoms are shown as ellipsoids at 30% probability.
Compound 2 displays K4OR4(OH2)2 polyhedra (see Figure 3). Individual
K4OR4(OH2)2 units are linked via secondary K-C interactions to afford a 1-D
coordination polymer (see Figure 4 and 5). Each K4OR4(OH2)2 core consists of
two edge sharing trigonal bipyramids, where the triply bridging oxygen atoms
16
form the apexes and the potassium atoms form the equatorial bases of the
pyramids. The K4OR4(OH2)2 cores display two unique potassium atoms. K(1)
and K(1A) are connected via four bridging oxygen units, two originating from the
Odpp ligands [O(1), O(1A): 2.710(2) and 2.723(2) Å] and two from a coordinated
water [O(3), O(3A): 2.836(2) and 2.969(2) Å]. K(2) binds to three oxygen
centers, two involve aryloxide ligands [K(2)-O(2): 2.642(2) Å; K(2)-O(1):
2.823(2) Å], and a water molecule with an unexpectedly short K-OH2 bond [K(2)O(2): 2.689(2) Å].
Table 3. Selected bond distances (Å) and bond angles (°) for {[K2(Odpp)2H2O]2}∞, 2.
K(1)-O(1)
2.723(2)
K(2)-O(1)
2.823(2)
K(1)-O(1A)
2.710(2)
K(2)-O(2)
2.642(2)
K(1)-O(3)
2.969(2)
K(2)-O(3)A
2.689(2)
K(1)-O(3)A
2.836(2)
K(1)-O(1)-K(2)
K(1)-O(1)-K(1A)
K(2)-O(1)-K(1A)
93.25(6)
85.85(5)
94.78(6)
O(3)-K(1)-O(1A)
O(3)-K(1)-O(3A)
69.03(6)
100.85(6)
K(1)-C(7)
K(1)-C(8)
K(1)-C(9)
K(1)-C(10)
K(1)-C(11)
K(1)-C(12)
K(1)-C(14A)
K(1)-C(15A)
3.208(3)
3.402(3)
3.520(3)
3.447(3)
3.248(3)
3.123(3)
3.086(3)
3.348(3)
K(1)-H(3A)
K(1)-H(3AA)
K(2)-H(3BA)
2.80(4)
2.68(4)
2.84(4)
K(1)-O(3)-K(1A)
K(1)-O(3)-K(2A)
K(1A)-O(3)-K(2A)
93.67(7)
91.94(7)
93.67(7)
K(2)-C(1)
K(2)-C(6)
K(2)-C(19)
K(2)-C(30)
K(2)-C(35B)
K(2)-C(36B)
3.093(3)
3.454(3)
3.443(3)
3.479(3)
3.107(3)
3.123(3)
Symmetry transformations used to generate equivalent atoms:
A: -x+1,-y+1,-z+1 B: -x,-y+1,-z+1
17
As a result of the short potassium-water distance further analyses were
made to confirm the identity of O(3) as water, and exclude misidentification as a
hydroxide. The Bond-Valence Sum (BVS) method utilized by Brese and O’Keefe
further supports our assertion that O(3) originates from a solvated water
molecule.17 BVS analyzes the bond distances to a particular atom, providing
information on bonding and can be used to determine if bonds are absent for a
structure. Analysis of O(1) and O(2) [ligand oxygen atoms] indicated that these
atoms have met coordinative saturation because the sum of the bond-valence is
close to 2; however, O(3) has a particularly low value of 0.49 valence units,
indicating that this oxygen likely contains bonds to other atoms. Furthermore,
analysis of the difference map located both hydrogen atoms that were included in
the refinement and provided the identification of water within the final structure.
Table 4. Bond Valence Sum Value for {[K2(Odpp)2H2O]2}∞, 2.
Atom
R(K-O)a
R(C-O)a
υ (K-O)b
υ(C-O)b
O(1)
2.723
0.21
2.823
0.16
2.710
0.22
1.318
1.22
Συc
1.82
O(2)
2.642
0.27
1.310
1.25
1.52
O(3)
2.699
2.841
2.973
0.23
0.16
0.11
0.49
a
b
c
bond distance in angstroms
bond-valence contribution for the indicated bond
sum of the bond-valence provided by indicated bond type
18
In agreement with 1, 2 also contains several K-C interactions; however,
the incorporation of two donor water molecules into the core of the structure
results in a decrease in K-C interaction and a more complex aggregation motif,
as coordinative saturation not only comes from K-C interactions, but also KO(donor) and K-H agostic interactions. While K(1) displays a formal
coordination number of four through contacts with water and ligand oxygen
atoms, the geometry of the core leaves one face of K(1) exposed allowing for
6:2 K-C interactions originating from the ortho phenyl rings. In addition to interactions, K(1) is also involved (in the solid state) in two K-H agostic
interactions [2.68(4) and 2.80(4) Å]. These compare well to those in
{[(Me3Si)2N]2V-N(SiMe3)SiMe2CH2]} {K(THF)2} 218 where K-H agostic
interactions were observed to be between 2.05-2.99 Å.18
K(2) is also involved in several K-C interactions, but in a more complex
bonding motif. A total of six -interactions were determined with an 2
interaction between the central aryloxide, an 1:1 to the ligand bonded to the
metal, and an 2 bonding motif to the neighboring K4(OR)4(OH2)2 core providing
the 1-D propagation. In addition, there is a single K-H agostic interaction
[2.84(4) Å] originating from the donor water molecule.
The quadruple bridge motif is very rare. A similar coordination pattern is
observed in the sodium aryloxide (NH3CH2CH2NH3){Na2[2(C6H4O2)2(C6H4OOH)2}, although the bridging ligands are bidentate.19 Both
compounds also display the common trend with bridging M-O distances about
~0.2 Å longer than the terminal ones. Structural similarities between the two
19
compounds also extend to the M-O-M angles with Na-O-Na angles between
70.58(7)-74.56(6)°, whereas in 2 the corresponding angle is slightly larger
[85.85(5)°], a difference that can be explained by the significant size difference
between Na and K.
4. Conclusions
The presence or absence of M-Cπ interactions has a significant impact on
molecular architecture. The low formal coordination numbers in both compounds
are supplemented by extensive K-C interactions. Water coordination has a
profound effect on the overall structural geometry and extent of -bonding. It is
of note that despite crystallization from THF, neither of the two compounds
coordinates THF, in contrast to the smaller water molecule. Apparently, water
coordination still allows for substantial K-C interactions, thus providing the
combined stabilizing effect of co-ligand and -coordination.
20
References:
(1)
Maria Felisa Zuniga; Glen B. Deacon; Karin Ruhlandt-Senge, New
structural features in heavy alkaline earth-metal chemistry- molecular
heterobimetallic group 1, Ba complexes, Chem.--Eur. J. 13, 1921 (2007).
(2)
Maria Felisa Zuniga; B. Deacon Glen; Karin Ruhlandt-Senge,
Developments in heterobimetallic s-block systems: synthesis and
structural survey of molecular M/Ae (M=Li, Na, K, Cs; Ae=Ca, Sr)
aryloxo complexes, Inorg. Chem. 47, 4669 (2008).
(3)
Glen B. Deacon; Peter C. Junk; Graeme J. Moxey; Karin Ruhlandt-Senge;
Courtney St. Prix; Maria F. Zuniga, Charge-Separated and Molecular
Heterobimetallic Rare Earth-Rare Earth and Alkaline Earth-Rare Earth
Aryloxo Complexes Featuring Intramolecular Metal-pi-arene Interactions,
Chem.--Eur. J. 15, 5503 (2009).
(4)
Glen B. Deacon; Alex Gitlits; Peter C. Junk; Brian W. Skelton; Allan H.
White, Synthesis and structures of homoleptic monomeric potassium
aryloxolanthanoidate(III) complexes, Z. Anorg. Allg. Chem. 631, 861
(2005).
(5)
G. B. Deacon; C. M. Forsyth; P. C. Junk, 2,6-Diphenylphenolates of
calcium, strontium and barium exhibiting -phenyl encapsulation of the
partially naked cations, J. Organomet. Chem. 607, 112 (2000).
(6)
Charles S. Weinert; Phillip E. Fanwick; Ian P. Rothwell, Synthesis of
Group 1 Metal 2,6-Diphenylphenoxide Complexes [M(OC6H3Ph2-2,6)]
(M = Li, Na, K, Rb, Cs) and Structures of the Solvent-Free Complexes
21
[Rb(OC6H3Ph2-2,6)]x and [Cs(OC6H3Ph2-2,6)]x: One-Dimensional
Extended Arrays of Metal Aryloxides, Inorg. Chem. 42, 6089 (2003).
(7)
J. M. A. Baas; H. Van Bekkum; M. A. Hoefnagel; B. M. Wepster, Note on
the selective tert-butylation of benzene and alkylbenzenes, Recl. Trav.
Chim. Pays-Bas. 88, 1110 (1969).
(8)
Hakon Hope, X-ray crystallography. A fast, first-resort analytical tool,
Prog. Inorg. Chem. 41, 1 (1994).
(9)
G. M. Sheldrick. SADABS, Program for Absorption Correction Using
Area Detector Data. 1996.
(10)
G. M. Sheldrick. SHELXTL-Plus, Program for Crystal Structure Solution
and Refinement. 1993.
(11)
Glen B. Deacon; Tiecheng Feng; Peter C. Junk; Brian W. Skelton; Allan
H. White, Homoleptic anionic aryloxolanthanoid(III) complexes, J. Chem.
Soc., Dalton Trans. 1181 (1997).
(12)
J. Hitzbleck; A. Verma; M. A. Guino-o; J. Gonzalez; K. Ruhlandt-Senge,
in prep.
(13)
R. D. Shannon, Revised effective ionic radii and systematic studies of
interatomic distances in halides and chalcogenides, Acta Crystallogr., Sect.
A. A32, 751 (1976).
(14)
Timothy J. Boyle; Nicholas L. Andrews; Mark A. Rodriguez; Charles
Campana; Timothy Yiu, Structural Variations of Potassium Aryloxides,
Inorg. Chem. 42, 5357 (2003).
22
(15)
Dennis A. Dougherty, Cation-pi interactions in chemistry and biology: a
new view of benzene, Phe, Tyr, and Trp, Science (Washington, D. C.).
271, 163 (1996).
(16)
CRC Handbook of Chemistry and Physics; 87 (CRC Press: Taylor and
Francis, 2006-2007).
(17)
Michael O'Keefe; N. E. Brese, Atom sizes and bond lengths in molecules
and crystals, J. Am. Chem. Soc. 113, 3226 (1991).
(18)
Mark Moore; Sandro Gambarotta; Corinne Bensimon, Serendipitous
Formation of a Dinuclear Vanadium(III) Amide Complex Containing a
Vanadaazacyclobutane Ring. Potassium-Hydrogen Agostic Interactions
Holding Together a V2K2 Tetrametallic Framework, Organometallics. 16,
1086 (1997).
(19)
Xiao-Ming Lu; Li Li; Fu-Gen Song; Bo Wang; Hua-Zhen Yuan; ChaoHui Ye, Structure and NMR spectroscopy in solid state and solution of
{Na2[2-(C6H4O2)2](C6H4OOH)2}4, Chin. J. Chem. 24, 336 (2006).