摘要:
Self-assembly motifs of palladium(II) dicarboxypyridine complexes Scheme 1 Results and discussion Zeng Quan Qin,a Michael C. Jennings,a Richard J. Puddephatt*a and Kenneth W. Muir*b a Department of Chemistry, University of Western Ontario, London, Canada N6A 5B7 b Department of Chemistry, University of Glasgow, Glasgow, UK G12 8QQ. E-mail: ken@chem.gla.ac.uk Received 23rd March 2000, Accepted 30th March 2000, Published 18th April 2000 trans-Dichlorobis(3,5-dicarboxypyridine)palladium(II), 1, and the analogous 2,6-dimethyl-3,5-dicarboxypyridine complex, 2, self-assemble through similar hydrogen bonding motifs which involve interactions between (i) the carboxylic acid substituents and solvate molecules (methanol or water) and (ii) hydroxy groups and chloride ligands.In the case of 1 these motifs give rise to a compact 2D polymeric network, whereas 2 forms a solid with high thermal stability containing well-defined channels. 2h) symmetry and 2 R (8) rings5 of the weakly bound benzonitrile ligands of trans- [PdCl2(NCPh)2] in THF by the corresponding ligand.† Both form pale yellow, air-stable solids which absorb water in air. In addition, 2 crystallizes from tetrahydrofuran as the solvate 2·2THF. Complexes 1 and 2 are soluble in THF, methanol and ethanol, while 2 is also soluble in acetone, and both 1 and 2 crystallize as water or alcohol solvates when this is possible, as described below. Crystals of 1 as the solvate 1·2MeOH were grown from methanol solution by slow evaporation (see Table 1).Each molecule of 1 [Fig. 1(a)] lies on an inversion centre and displays the expected trans-[PdCl2L2] structure. The two pyridine rings are nearly normal to the PdN2Cl2 coordination plane [Cl–Pd–N–C torsion angle 88.1(3)°]. The C7 and C10 carboxy groups each lie in the plane of the pyridine ring to which they are bonded but they are oriented differently, their hydroxy groups being respectively syn and anti with respect to the Pd atom. The intermolecular association is complex and interesting [Fig. 1(b)]. Two C10 carboxylic acid groups related by an inversion centre take part in hydrogen bonding mediated by methanol molecules to give a zig-zag chain structure in which adjacent Pd atoms are 15.88 Å apart, being related by the lattice vector [201]. Association by insertion of pairs of hydroxylic solvent molecules between pairs of carboxylic acid groups to form planar, homodromic and usually centrosymmetric 4 4 R (12) rings (Scheme 1, 5) has been exploited in clathrate design,6d though it has not previously been observed in inorganic complexes.2d,6 The zig-zag chains pack parallel to one another and pairs of Pd atoms in adjacent chains are interlinked by hydrogen bonding between C7 carboxylic acid groups and chloride ligands.Centrosymmetric (Pd–Cl···H–OC3N)2 R2 (16) rings containing pairs of Pd atoms related by the vector [110] are thereby formed. Since the chloride ligands of each PdCl group hydrogen-bond to carboxylic acid groups of different zig-zag chains, the combination of the two hydrogenbonding schemes leads to the corrugated 2D sheet structure shown in Fig.1(b). The overall structure is compact and there are no cavities which might give rise to further solvent inclusion. Complex 2 was recrystallized from acetone by slow evaporation in air to give the solvate 2·4H2O, and Introduction There has been increasing interest in the design and preparation of supramolecular assemblies by crystal engineering, using intermolecular forces such as hydrogen bonding to assemble the building blocks.1,2 A recent advance involves the inclusion of coordination complexes into the building blocks, since the metal ion can act as a template for pre-assembly of two or more functional groups with predictable geometrical form.2,3 Although hydrogen bonding has been shown to promote self-assembly of inorganic and organometallic compounds with notable efficiency,3,4 relatively little has been done to exploit the capability of the carboxylic acid groups to hydrogen bond by incorporating them as substituents in coordination compounds so as to obtain supramolecular architectures.4 It has been shown that linear polymers may be self-assembled from complexes such as trans-[PdCl2{NC5H4(CO2H-4)}2] through intermolecular hydrogen bonding between the carboxy substituents.4a We now demonstrate that a restricted repertoire of hydrogen bonding motifs determines how polymeric structures can be self-assembled from transdichloropalladium(II) complexes of 3,5-dicarboxypyridine ligands, 1 and 2, Scheme 1.There is a clear topological resemblance between 1 or 2 and the alkyne derivative 3 (Scheme 1), which forms a 2D sheet structure in the solid state, each molecule showing near 2/m (C linking to four others through the familiar 2 the carboxylic acid dimer structure (Scheme 1, 4).2e Compounds 1 and 2 were synthesized by displacement of DOI: 10.1039/b002305l CrystEngComm, 2000, 11 2 2(a) (b) Fig. 1 (a) The structure of 1. Click the image or here for a 3D view. Here and in Fig. 2(a) 50% probability ellipsoids are shown for all non-H atoms. Symmetry code: –x, –y, –z. (b) A part of the sheet structure formed by hydrogen bonding. The approximate directions of the lattice vectors [201] and [110] which relate Pd atoms connected by the two principal hydrogen bonding motifs are respectively horizontal and vertical.Selected distances (Å) and angles (°) in 1: Pd–N 2.005(3), Pd–Cl 2.301(1), N–Pd–Cl 91.7(1), O12H···O21 [H···O 1.71, O···O 2.526(5), O–H···O 169]; O21H···O11 [H···O 1.87, O···O 2.665(5), O–H···O 161] and O9H···Cl [O···Cl 3.087(3)]. Click image or here for a 3D view. Table 1 Crystal data for palladium(II) dicarboxypyridine complexesa Properties Formula MCrystal system Space group a/Å b/Å c/Å /° /° /° V/Å3 Dc /g cm–3 Z/mm–1 T/K Unique reflections R1 (all data) a Click here for full crystallographic data (CCDC no. 1350/17). 1·2MeOH 2·4H2O C16H18Cl2N2O10Pd 575.62 Triclinic C18H26Cl2N2O12Pd 639.71 Monoclinic C2/m P 1 0.891 150(2) 1594 0.047 4.9006(4) 11.625(2) 7.9416(9) 20.765(4) 14.285(2) 6.5940(10) 97.815(6) — 99.871(6) 116.12(3) 100.030(6) — 531.42(9) 1429.2(4) 1.799 1.487 1 2 1.181 215(2) 3043 0.074(a) (b) (c) Fig.2 (a) The structure of 2. Symmetry code: –x, y, –z; –x, –y, –z; x, –y, z. Click the image or here for a 3D view. (b) The formation of an 44 R (12) ring by molecules whose Pd atoms are connected by the lattice vector [1/2,1/2, –1]. The two molecules on the right hand side are related by translation along c and are linked via hydrogen bonds from the same water molecule. Click image or here for a 3D view. (c) The porous sheet structure formed by intermolecular hydrogen bonding viewed in projection down the c-axis.Traces of acetone present in the channels are not shown. Selected distances (Å) and angles (°) in 2: Pd–N 2.063(3), Pd–Cl 2.311(2), N–Pd–Cl 90, O2H···O3 [H···O 1.62, O···O 2.579(3), O–H···O 174], O3H···O1 [H···O 2.01, O···O 2.795(3), O–H···O 174], O3H···Cl [O···Cl 3.273(3)]. Click image or here for a 3D view. there is also evidence for disordered organic solvent molecules in the crystals (see Table 1). The molecules of 2 [Fig. 2(a)] display exact 2/m (C2h) symmetry. They closely resemble those of 1 despite the steric crowding which arises from adding two extra methyl substituents to each pyridine ring: thus, these rings are tilted by only 6° from exact orthogonality with the PdN2Cl2 coordination plane. The Pd–N bonds in 2 are 0.06 Å longer than those in 1, thereby helping to relieve short intramolecular H···H and Pd···H contacts of 2.3 and 2.6 Å,respectively, involving tthere he hydrogen atoms of the C4 methyl groups.Crystallographic symmetry requires the four carboxy groups to be equivalent. In contrast to 3, where the four carboxy groups are protonated syn to the molecular cent roid, th e OH groups in 2 are all anti to the Pd atom, as is shown by the C1–C2–C5–O2 torsion angle of –169.1(3)°. Each takes part in hydrogen bonding mediated by water molecules, thereby forming slightly puckered, centrosymmetric 44 R (12) rings [Fig. 2(b)]. The Pd atoms in molecules so connected are related by the lattice vector [1/2,1/2, –1] and are 14.79 Å apart — slightly closer than in 1.The water molecules also take part in weak hydrogen bonding to the chloride ligands. The final outcome of the self-assembly process is the formation of stacks of molecules related by translation along the c-axis. Adjacentmolecules of 2 within each stack are held together by accepting Cl···HO(water) and C=O···HO(water) hydrogen bonds from the same water molecule, while the 4 4 R (12) rings link each stack to its four nearest neighbours. Channels running parallel to c are thereby formed [Fig. 2(c)] which are large enough (144 Å3 per cell) to accommodate disordered molecules of acetone.7 The nature of the hydrogen bonding network in 2 suggests that the solid should be resistant to degradation by heating. This expectation is fulfilled: thermogravimetric analysis indicated no weight loss on heating to 200 °C, and only ~4% weight loss at 260 °C; the decomposition temperature was 264 oC.This high thermal stability could lead to use of 2 as a porous material. Conclusions This work shows that easily prepared palladium complexes trans-[PdCl2L2], where L is a pyridine derivative containing two carboxylic acid substituents, use the same hydrogen-bonding motifs, namely the 4 4 R (12) ring incorporating a hydroxylic solvent (MeOH or H2O) and Pd–Cl···H–O linkages, to self-assemble. In each solid all carboxy and hydroxy OH groups participate as donors in hydrogen bonds, and all chloro ligands and carbonyl oxygen atoms, except for O8 in 1, act as hydrogen bond acceptors. Despite this, the patterns observed in complexes 1 and 2 are each different and unique and contrast with that exhibited by alkyne 3 which lacks acceptor groups corresponding to the chloro ligands of complexes 1 and 2 but otherwise is topologically similar to them.Factors important in permitting 1–3 to self-assemble in such different ways include the ability of each carboxy group to adopt two possible orientations relative to the molecular centroid and the possibility of incorporating molecules of hydroxylic solvate in the solid. These factors make the difficulty of predicting the outcome of such experiments only too apparent. Despite this we are encouraged that this simple synthetic method for crystal engineering of porous materials has led to the successful production of 2.Acknowledgements RJP and KWM thank, respectively, the NSERC (Canada) and the EPSRC (UK) for financial support. KWM also thanks Dr S. J. 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Ibers, Acta Crystallogr., Sect. B, 1969, B25, 2423; (d) E. Weber, I. Csoregh, B. Stensland and M. Czugler, J. Am. Chem. Soc., 1984, 106, 3297. 7 This estimate of the free space exterior to the van der Waals envelopes of the atoms of the molecules of 2 and water was made with A. L. Spek's program PLATON. (a) A. L. Spek, Acta Crystallogr., Sect A: Fundam. Crystallogr., 1990, 46, C34; (b) A. L. Speck, PLATON, A Multipurpose Crystallographic Tool, Utrecht University, Utrecht, 1998. Footnote (13C) = 165.0 [CO † Selected NMR data: 1 in CD (1H) = 9.54 [d, 3OD, 4J(HH) = 2 Hz, 4H, H2,6]; 8.94 [t, 4J(HH) = 2 Hz, 2H, H4]; 2H], 158.3 [C2], 141.6 [C3], 130.0 [C4]; 2·2THF in acetone-d6, (1H) = 8.84 [s, 2H, H4]; 4.13 [s, 12H, Me]; 12.01 [b, 4H, COOH]; 3.62, 1.79 [m, THF]; (13C) = 165.8 [CO2H], 165.4 [C2], 143.4 [C3], 127.2 [C4], 26.8 [Me], 68.0, 26.1 [THF]. Satisfactory C, H and N analyses were obtained for both new complexes. CrystEngComm © The Royal Society of Chemistry 2000
ISSN:1466-8033
DOI:10.1039/b002305l
出版商:RSC
年代:2000
数据来源: RSC