Download Alcohol responsive 2D coordination network of 3

318
Z. Kristallogr. 2013, 228, 318–322 / DOI 10.1524/zkri.2013.1607
# by Oldenbourg Wissenschaftsverlag, München
Alcohol responsive 2D coordination network
of 3-(4-pyridyl)benzoate and Zinc(II)
Gift Mehlana, Gaëlle Ramon and Susan A. Bourne*
Centre for Supramolecular Chemistry Research, Department of Chemistry, University of Cape Town, Rondebosch 7701, South Africa
Received February 8, 2013; accepted May 14, 2013
Published online: July 1, 2013
Coordination network / Guest exchange /
Thermal analysis / Alcohol sorption
Abstract. The solvothermal reaction of 3-(4-pyridyl)benzoic acid and zinc nitrate yielded a 2D network with
an sql topology. Both elemental analysis and single crystal
X-ray diffraction studies confirmed the formula of the
compound as {[Zn(34pba)2] (0.5 DMF) (0.5 H2O)}n (1).
At room temperature, the desolvated phase of 1, 1d, absorbs methanol, ethanol, 1-propanol and 1-butanol but not
water vapour.
1. Introduction
One of the most important objectives in the field of coordination networks or metal organic frameworks is the engineering of porous structures with a well defined chemical environment [1–2]. This is however very difficult to
achieve in 3D structures due to catenation and interpenetration. Thus in recent years, solid state chemists have developed a series of bottom-up fabrication schemes to
achieve two-dimensional open coordination networks, frequently with limited domain size, using non covalent interactions such as hydrogen bonding [3], metal directed assembly [4], and the organisation of flexible species [5].
Porous materials based on 2D frameworks have received
attention owing to useful properties endowed by dynamic
guest- responsive phenomena [6]. The interlayer separation
plays a major role in guest inclusion while framework
flexibility can be achieved as a result of sliding of the 2D
layers. Most importantly the ability of the framework to
open or close its channels upon exposure to guest molecules has high potential for realising new useful functions,
such as switching and sensing [7].
2D metal organic frameworks can be created by combining bifunctional ligands coordinated meridially to a trigonal bipyriramidal or octahedral node [8–10]. To create
such a system, we have focussed on an asymmetric ditopic ligand, 3-(4-pyridyl)benzoic acid, expecting that both
the pyridyl and the carboxylate moiety would coordinate
* Correspondence author (e-mail: [email protected])
to the metal center. Variation in the dihedral angles between the pyridyl and the benzene ring was also expected
to contribute towards framework flexibility while maintaining structural integrity. Finally, we chose the Zn(II) metal
ion as it can adopt different geometries due to its versatile
coordination chemistry.
2. Experimental
All materials were purchased from commercial sources
and were used without further purification.
2.1 Synthesis:
{[Zn(34pba)2] (0.5 DMF) (0.5 H2O)}n
Zn(NO3)2 6 H2O (29 mg, 0.1 mmol) was dissolved in
4 ml of water. 3-(4-pyridyl) benzoic acid was dissolved in
4 ml dimethyl formamide (DMF) with heating and stirring. The two solutions were combined in a 25 ml teflon
lined autoclave and sealed tightly. The mixture was then
heated (ca. 2 C min1) at 105 C for 72 hours. Colourless
block crystals were formed upon cooling (ca. 1 C min1)
the reaction mixture to room temperature. Elemental analysis. % Calculated for C25.5H20.5N2.5O5Zn, C ¼ 60.36,
H ¼ 4.07, N ¼ 6.90. % Found C ¼ 60.40, H ¼ 3.99,
N ¼ 6.06
2.2 Crystal structure determination
Crystal structure determination by single crystal X-ray diffraction was performed using a Bruker ApexII KAPPA
CCD diffractometer at 173 K using a graphite monochoromated MoKa radiation (l ¼ 0.71073 A). Unit cell refinement and data reduction were achieved using the program
SAINT [11]. The data was corrected for Lorentz- polarisation effects and absorption using the SADABS [12] program. The structure was solved by direct methods and refined using the SHELXL [13] computer programme
package within the X-SEED [14] interface. Except for hydrogen atoms and atoms of the disordered DMF molecule,
all atoms were refined anisotropically. Hydrogen atoms
were introduced at calculated positions and refined isotropically. The bond angles and bond distances of the disorUnauthenticated
Download Date | 6/12/17 7:22 AM
319
Alcohol responsive 2D coordination network of 3-(4-pyridyl)benzoate and Zinc(II)
dered DMF molecule were fixed based on the average values found from the Cambridge structural Database [15].
Crystal data: Mr 507.34 g mol1, Monoclinic, space
group C2/c, a ¼ 21.3002(4) Å, b ¼ 11.6040(2) Å, c ¼
21.499(4) Å, b ¼ 118.70(3) , V ¼ 4661.0(16) Å3, Z ¼ 8,
crystal size(mm) ¼ 0.200.250.33, 28437 reflections
measured, No of unique relections ¼ 5338, No of unique
reflections with I > 2q ¼ 4770. The final R values were
R1 ¼ 0.0435, wR2 ¼ 0.1323, Max, min electron density
(e A3) 2.54 (in the region of the disordered DMF molecule), 0.57. The structure was deposited at the CCDC and
allocated the number CCDC 923522.
found to be 424.64 and [4.4.4.4.4.4.4.4.4.4.4.4.43.43.43.*.*.*]
respectively. The topological density value (TD 10) was
found to be 221. The relevant outfiles are given in the Supporting information.
2.8 Sorption studies
Compound 1 was activated by heating under a vaccum for
5 hrs at 130 C to generate 1d. 1d was placed in small
open vials. The small vials containing the activated samples were then placed in large vials containing respective
dry solvents. The large vials were capped and sealed
tightly before being left at room temperature for 24 hours.
2.3 Powder X-ray diffraction (PXRD)
Powder X-ray diffraction measurements were performed
on a BRUKER D8 Advance X-ray diffractometer using.
CuKa-radiation (l ¼ 1.5406 Å). Samples were placed on a
zero background sample holder and scanned over the
range of 4 to 30 with a step size of 0.01 per second at
an accelerating voltage of 30 kV and a current flow of
40 mA. For variable temperature studies, samples were
placed in a capillary rotation device on a HUBER Imaging
Plate Guinier Camera 670 fitted with a HUBER HighTemperature Controller HTC 9634 unit. Ni-filtered CuKaradiation (l ¼ 1.5406 Å) was used to measure the PXRD
patterns at elevated temperatures.
2.4 Hot stage microscopy
The behaviour of the compounds was monitored using a
Nikon SMZ-10 stereoscopic microscope fitted with a Linkam THMS600 hot stage and a Linkam TP92 control unit.
The samples were placed on a transparent glass slide and
covered in silicon oil. The compound was heated from 25
to 400 C at heating rate of 10 C min1. The images
were captured at different temperatures using a Sony Digital HAD colour video camera and recorded using the Soft
Imaging System program [16].
3. Results and discussion
3.1 Structural description
X-ray single crystal structure analysis revealed that the
compound crystallizes in the monoclinic space group
C2=c. The asymmetric unit (shown in Scheme 1) consists
of one Zn (II) ion, two deprotonated ligands (34pba), half
uncoordinated water molecule and a disordered half DMF
molecule sitting on a two-fold axis at Wyckoff position e.
The Zn(II) centre is coordinated to three oxygen atoms
from the 34pba carboxylate groups with bond distances
ranging from 1.974 (2) Å to 2.315(2) Å and two nitrogen
atoms with distances of 2.093(2), (Zn1––N1B) and
2.010(2) Å, (Zn1––N1A). The relevant bond lengths and
bond angles are given in the supporting information (Tables S1 and S2).
2.5 Differential Scanning Calorimetry (DSC)
In order to determine the onset temperature of guest loss
DSC was performed. The sample was dried on filter paper
and a sample of 0.5–1 mg placed in ventilated aluminium
pans with lids and heated at 10 C min1 under nitrogen
gas flow (50 mL min1). The experiment was performed
using a TA instrument DSC-Q200.
2.6 Thermogravimetric analysis (TGA)
Thermogravimetric analyses were performed using a TA
Instrument TAQ-500. Samples of 1–2 mg were heated at
10 C min1 under nitrogen gas flow (50 mL min1).
2.7 Topological analysis
The netwok topology of the compound was analysed using
X-SEED, SYSTRE [17] and TOPOS [18] and checked
against the Reticular Chemistry Structural Resource (RSCR)
[19]. The calculated point symbol and vertex symbol were
Scheme 1
The overall geometry around the Zn(II) centre is trigonal
bipyramidal. The 3-(4-pyridyl) benzoate ligands show different coordination modes, that is they adopt a tridentate
m2-bridging and bidentate m2-bridging modes. The dihedral
angles between the pyridyl and benzene ring in the ligands are 23.2(1) and 32.7(4) for the ligand with tridenUnauthenticated
Download Date | 6/12/17 7:22 AM
320
G. Mehlana, G. Ramon and S. A. Bourne
Fig. 1. Coordination environment of the Zn(II) centre displaying the binding modes assumed by the carboxylate moiety. Hydrogen atoms have
been omitted for clarity.
a
a
b
b
Fig. 2. (a) Packing diagram of the compound viewed along [010].
The diagram illustrates interdigitated 2D layers in the channels of
which water and DMF guest molecules (van der Waals radii) reside,
(b) packing diagram as viewed along [001].
tate m2-bridging mode and bidentate m2-bridging mode respectively. The tridentate m2-bridging mode (equatorial position) and bidentate m2-bridging mode (axial position) act
as linear linkers to join two zinc centres with Zn––Zn of
11.6(5) Å and 10.8(3) Å respectively giving rise to a 2D
coordination network (Fig. 1).
These 2D layers are stabilised by non classical hydrogen bonds (Table 1) which connect them together.
The 2D layers are interdigitated encapsulating water
and DMF as guest molecules in channels (Fig. 2).
Extensive hydrogen bonding interactions exist between
water and DMF guest molecules, however there are no
c
Fig. 3. (a) Network connectivity of the compound. (b) Network analysis of the compound. Spheres represent the 4-connected uninodal
node at each Zn(II) center. (c) Four-fold non interpenetrating parallel
sql nets.
hydrogen bonding interactions between the solvent molecules and the 2D framework.
The solvent accessible void volume in the solvent free
network was determined using the SQUEEZE routine in
Platon [20] as 846.7(5) Å3 which is approximately 19% of
the unit cell volume. Topological analysis of the compound revealed a 4-connected uninodal sql grid net. The
Symmetry operator
d(C O) (Å)
Angle ( )
C5A––H5A O14B
C6B––H6B O15B
3
=2 x, 1=2 þ y, 1=2 z
x, 1 þ y, z
3.112(3)
3.142(3)
132
119
C12B––H12 O14B
2 x, y, 1=2 z
2.829(3)
100
Table 1. Weak hydrogen bonding intramolecular interactions.
Unauthenticated
Download Date | 6/12/17 7:22 AM
321
Alcohol responsive 2D coordination network of 3-(4-pyridyl)benzoate and Zinc(II)
Table 2. TGA analysis for 1 and the resulting alcohol inclusion compounds from sorption studies.
Fig. 4. An overlay of the TGA and DSC for 1.
TGA Experimental
mass loss %
Network/solvent
ratio 1 based on
Zn(34pba)2 : x
1
9.80
1 : 0.5 : 0.5
1d
1d-methanol
––
*
––
1d-ethanol
6.55
1 : 0.70
1d-1-propanol
8.75
1 : 0.74
1d-1-butanol
8.25
1 : 0.58
1: The network : solvent ratios were calculated using experimental results of the TGA for all the compounds. The results were modelled
on {[Zn(34pba)2] : solvent}n and expressed as 1 : x.
*: 1d-methanol stoichiometry could not be determined as the solvated
phase is not stable at room temperature.
packing diagram of the nets shows a four-fold non-interpenetrating sql nets as illustrated in Fig. 3.
3.2 Thermal analysis and sorption studies
Fig. 5. Variable temperature PXRD of the compound illustrating the
phase change that takes place between 250 and 290 C upon heating.
Thermal analysis by TGA shows that the compound is
stable at room temperature (Fig. 4). An initial weight loss
of 9.80% is observed over a temperature range of 90–
250 C which corresponds to loss of both the water and
the DMF from the host framework. This weight loss is a
reasonably good match to the solvent content modelled in
the crystal structure (calc: 8.90%). However, we have
noted that the 0.5 DMF molecules modelled per formula
unit in the crystal structure may be too low, as both the
TGA results and the % N in the elemental analysis support a higher guest occupancy. This may indicate that
guest occupancy varies between single crystals.
Fig. 6. PXRD of 1, 1d, the alcohol inclusion
compounds (1d-methanol, 1d-ethanol, 1d-propanol and 1d-butanol) and 1d-water.
Unauthenticated
Download Date | 6/12/17 7:22 AM
322
Decomposition of the guest-free compound occurs
above 380 C. The DSC shows two endotherms at 135
and 230 C which corresponds to successive release of
water and DMF molecules from the host channels. The
DSC analysis also displays an exotherm after complete
loss of guest molecules at approximately 280 C. This
event is further supported by variable temperature PXRD
studies which show that the compound undergoes phase
transformation between 250 and 290 C (Fig. 5).
Sorption studies were carried out as described in the
experimental section. The PXRD of the desolvated phase
is very similar to that of the as-made compound (Fig. 6)
which is an indication that structural integrity is maintained after desolvation. We confirmed that desolvation
had taken place by means of TGA. The activated sample
(1d) was exposed to solvent vapours (water, methanol,
ethanol, 1-propanol or 1-butanol) at room temperature in a
controlled environment. The amount of the solvents absorbed is given in the supporting information in Table 2
and in Figs. S1–S5. Interestingly the activated phase absorbed the alcohols but did not absorb water as evidenced
by no change in the diffraction pattern of the desolvated
phase on exposure to water vapour. This result is further
supported by TGA which is featureless until decomposition, indicating that no water was absorbed. Similar results
have been reported using a square-grid Cd(II) MOF [21]
and a lanthanide-carboxylate-MOF [22]. Figure 6 shows
the PXRD traces of the resultant alcohol inclusion compounds. The alcohol inclusion compounds exhibit diffraction peaks at lower 2q values than 1 and 1d. This is due
to the expansion of the 2D layers to accommodate guest
molecules. The ability of the ligand to vary its dihedral
angle by the rotation of the benzene and pyridyl rings
may help to explain why alcohol molecules are able to
move into the host framework.
4. Conclusions
A novel 2D compound with an sql net based on 34pba
and Zn(II) was synthesised and its properties evaluated.
Structural integrity is maintained upon desolvation and the
compound undergoes a structural rearrangement above
250 C. The dried phase of the compound absorbs alcohols at room temperature. This has been attributed to the
presence of open metal sites and the ability of the 2D
layers to glide past one another allowing for the entry of
guest molecules. The failure of the compound to absorb
water at room temperature also reveals its selective nature.
Acknowledgements. Funding for this project was received from the
South African National Research Foundation and the Swedish International Development Agency (SIDA). G.M. is grateful for the financial support he received from the University of Cape Town Chemistry
Equity Development programme and University of Cape Town 2013
JW Jagger Centenary Gift Scholarship.
G. Mehlana, G. Ramon and S. A. Bourne
References
[1] O. M. Yaghi, M. O’Keeffe, N. W. Ockwig, H. K. Chae, M. Eddaoudi, J. Kim, Reticular synthesis and the design of new materials. Nature 2003, 423, 705–714.
[2] Kitagawa, S. Kitaura, R. Noro, S. Functional porous coordination polymers. Angew. Chem. Int. Ed. 2004, 43, 2334–2375.
[3] S. Griessl, M. Lackinger, M. Edelwirth, M. Hietschold, W. M.
Heckl, Self-assembled two-dimensional molecular host-guest architectures from trimesic acid. Single Molecules 2002, 3, 25–31.
[4] A. Dmitriev, H. Spillmann, N. Lin, J. V. Barth, K. Kern, Modular assembly of two-dimensional metal-organic coordination networks at a metal surface. Angew. Chem. Int. Ed. 2003, 42,
2670–2673.
[5] G. Schull, L. Douillard, C. Fiorini-Debuisschert, F. Charra,
F. Mathevet, D. Kreher, A.-J. Attias, Single-molecule dynamics
in a self-assembled 2D molecular sieve. Nano Lett. 2006, 6,
1360–1363.
[6] S. J. Ghosh, W. Kaneko, D. Kiriya, M. Ohba, S. Kitagawa, A bistable porous coordination polymer with a bond-switching mechanism showing reversible structural and functional transformations. Angew. Chem. Int. Ed. 2008, 47, 8843–8847.
[7] E. J. Cussen, J. B. Claridge, M. J. Rosseinsky, C. J. Kepert,
Flexible sorption and transformation behaviour in a microporous
metal-organic framework. J. Am. Chem. Soc. 2002, 124, 9574–
9581.
[8] B. Ye, M. L. Tong, X. M. Chen, Metal-organic molecular architectures with 2,20 -bipyridyl-like and carboxylate ligands. Coord.
Chem. Rev. 2005, 249, 545–565.
[9] A. J. Fletcher, K. M. Thomas, M. J. Rosseinsky, Flexibility in
metal-organic framework materials: Impact on sorption properties. J. Sol. State Chem. 2005, 178, 2491–2510.
[10] S. Horike, D. Tanaka, K. Nakagawa, S. Kitagawa, Selective
guest sorption in an interdigitated porous framework with hydrophobic pore surfaces. Chem Commun. 2007, 3395–3397.
[11] SAINT, Version 7.60a; Bruker AXS Inc: Madison, WI, USA,
2006
[12] G. M. Sheldrick, SADABS, Version 2.05, 2007.
[13] G. M. Sheldrick, SHELXL-97, Program for crystal structure
solution, 1997.
[14] L. J. Barbour, X-Seed: A software tool for supramolecular crystallography. J. Supramol. Chem. 2001, 1, 189–191.
[15] F. H. Allen, The Cambridge Structural Database: a quarter of a
million crystal structures and rising. Acta Crystallogr., Sect. B.
2002, 58, 380–388.
[16] Soft Imaging System GmbH: Digital solutions for Imaging and
Microscopy, Version 3.1 for Windows, # 1987–2000.
[17] O. D. Friedrichs, SYSTRE 1.1.4beta, http://gavrog.org/, 2013.
[18] V. A. Blatov, V. Peskov, Acta Crystallogr. Sect. B. A comparitive
crystallochemical analysis of binary compounds and simple anhydrous salts containing pyramidal anions LO3 (L¼S, Se, Te, Cl,
Br, I). 2006, 62, 457–466; V. A. Blatov, Ac. Pavlov St. 1, 443001,
Samara, Russia, TOPOS 4.0, http://www.topos.ssu.samara.ru/,
accessed May 2012.
[19] M. O’Keeffe, M. A. Peskov, S. Ramsden, O. M. Yaghi, The Reticular Chemistry Structure Resource (RCSR) database of, and symbols for, crystal nets. Acc. Chem. Res. 2008, 41, 1782–1789; Reticular Chemistry Structure Resource, http://rcsr.anu.edu.au/, 2009.
[20] A. L. Spek, Structure validation in chemical crystallography.
Acta Crystallogr., Sect. D. 2009, 65, 148–155.
[21] T. Borjigin, F. Sun, J. Zhang, K. Cai, H. Ren, G. Zhu, A microporous metal-organic framework with high stability for GC separation of alcohols from water. Chem. Commun. 2012, 48,
7613–7615.
[22] Z. Lin, R. Zou, J. Liang, W. Xia, D. Xia, Y. Wang, J. Lin,
T. Hu, Q. Chen, X. Wang, Y. Zhao, A. K. Burrell, Pore sizecontrolled gases and alcohols separation within ultramicroporous
homochiral lanthanide–organic frameworks. J. Mater. Chem.
2012, 22, 7813–7818.
Unauthenticated
Download Date | 6/12/17 7:22 AM