CrystEngComm, 2000, 24 A porous one-dimensional coordination polymer composed of edge-shared hexagonal supramolecular units is allowed to diffuse slowly into the alcoholic solution at room temperature. The initial product after a period of approximately two weeks is a layered phase based on puckered sheets of hexagons, which has been previously reported.22 Upon further exposure to pyridine this phase dissolves after about two months and deep blue cubic blocks of 1 are obtained after approximately six months. Powder X-ray diffraction shows that after this period only phase 1 is present in the reaction vessel. Single crystal X-ray diffraction data were recorded on a Stoe-IPDS diffractometer at 193 K using graphite monochromated Mo-Ka radiation (a = 0.71073 Å).The crystal was mounted on glass fibre and quench cooled in a compressed air cryostream. 100 images were collected employing successive 2° rotations in f . Data were reduced using the Stoe IPDS software suite. The space group was determined from the systematic absences as Cc or C2/c. No meaningful solution was found in Cc. The structure was solved in C2/c using Direct Methods within SHELXS-86 (ref. 24) and subsequent Fourier synthesis in SHELXL- 97.25 Full matrix least squares refinement on F2 was carried out using SHELXL-97.25 Details of crystallographic work are given in Table 1. Powder X-ray diffraction data were recorded on a Stoe STADI P diffractometer operating in Debye–Scherrer geometry, using samples loaded in 0.3 mm glass capillaries, Cu Ka1 radiation from a curved Germanium monochromator, and a linear position sensitive detector.T. J. Prior and M. J. Rosseinsky* Department of Chemistry, University of Liverpool, Liverpool, UK L69 7ZD. E-mail: m.j.rosseinsky@liv.ac.uk Received 29th June 2000, Accepted 2nd August 2000, Published 14th August 2000 A one-dimensional coordination polymer derived from edge-shared hexagonal units is reported. Each hexagon is composed of six nickel(II) cations linked by 1,3,5-benzenetricarboxylate. The ribbons of hexagons are held together by hydrogen bonding interactions through free carboxylic acid units. Large pores (ca. 33% of the crystal volume) exist within the crystal structure. These are filled with disordered butan-1-ol, which may be removed by heating to 150 °C resulting in framework collapse.Coordination polymers1 have been widely studied in attempts to mimic the diverse chemistry displayed by classical porous materials such as the aluminosilicates and their analogues.2 One particular aspect of work which has attracted a lot of attention in this burgeoning field is the design of materials with specific properties by careful choice of starting materials. Indeed there are now many examples of tailored materials which mimic known structure types.1(b),3 The (6,3) plane net4 (often called the honeycomb network) is one particularly common structural topology found in a wide variety of examples. The honeycomb sheet represents the most efficient way of covering a plane surface. As far back as the 4th century AD this was believed to be the case.† Honeycomb sheets are observed in metal–cyanide networks5 and a variety of other systems.6 Puckered ribbons of hexagons are also known.7 The anion of the tridentate 1,3,5-benzenetricarboxylic acid (sometimes called trimesic acid), btc, has attracted considerable attention as a potential building block for molecular frameworks.The anhydrous acid crystallises with a structure composed of interpenetrating honeycomb networks.8 Honeycomb sheets are also observed when it is crystallised with suitable aliphatic bases.9 A wide range of structures are known which display btc anions joined by transition 10 and main group11,12 metals. These include one- ,13–15 two-,16–19 and three-dimensional20,21 structures.We have recently shown that choice of solvent, in particular its bulk and hydrophilicity, allows manipulation of hydrogen bonding around a metal centre thereby affording control over the orientation of btc anions about the metal. In this way honeycomb sheets22 and porous enantiopure chiral networks23 with stoichiometry M3(btc)2 may be obtained. Here we demonstrate that one-dimensional architectures may be obtained by control of the reaction conditions. Experimental Butan-1-ol was obtained from BDH and all other reagents were obtained from the Aldrich Chemical Company. All were GPR grade and used as supplied. Ni(NO3)2 · 6H2O (0.5g, 1.72 mmol) and H3btc (0.25g, 1.19 mmol) were dissolved in 100 ml of butan-1-ol in an Erlenmeyer flask.Pyridine (4 ml, 50 mmol) was placed in a test-tube which was sealed with parafilm and this seal pierced with a pinprick. The test-tube was placed in the Erlenmeyer flask, which was then sealed with parafilm. In this way pyridine DOI: 10.1039/b005236l Results 1 crystallises in the space group C2/c (no. 15) (see Table 1 for crystallographic data). Chemical analysis is approximately consistent with the composition obtained crystallographically: for Ni5(btc)2(Hbtc)2(C5H5N)15(H2O)5 · xC4H9OH · yH2O · zC5H5N where x ß 9.2, y ß 6, z ß 2.2, calculated % C 56.7, H 6.42, N 7.16, Ni 8.72; found % C 56.8, H 5.89, N 7.16, Ni 8.73. 1 is a one-dimensional coordination polymer containing ribbons of edge-sharing hexagons.Each hexagon is composed of a total of 48 atoms, six octahedral NiII ions joined by six btc anions, and has a mean side of 11.33(1) Å (defined as the distance between btc centroids). Each nickel acts as a linear connector to two trans btc units. The octahedral coordination is completed by three pyridine and one water molecule. This water molecule forms two hydrogen bondsTable 1 Crystallographic data for 1a Compound Formula FW/g mol–1 T/K l/Å Colour Morphology Size/mm3 Crystal system Space group a/Å b/Å c/Å a/° b/° g/° V/Å3 Zrcalc/Mg m–3 m/mm–1 2 qmax/° Data/restraints/parameters R(F) (%) I > 2 s(I), {all data} Rw(F2) (%) I > 2 s(I), {all data} GOF a Click here for full crystallographic data (CCDC No.1350/30). to the trans carboxylates. An ORTEP26 diagram is shown in Fig. 1. There are two different modes of coordination displayed by the btc anions. Where adjacent hexagons share an edge, the btc units at the ends of this edge each bind to three NiII ions in monodentate fashion (Fig. 2). The remaining vertices of the hexagons are occupied by btc bridging two NiII cations. The third acid functionality of these two btc units is not deprotonated. These hexagonal supramolecular units join together through a common edge to generate infinite one-dimensional ribbons that are one hexagon wide. (Fig. 3) Fig. 1 ORTEP plot of the asymmetric unit of 1 with atoms drawn as 50% thermal ellipsoids. For the sake of clarity solvent molecules and hydrogen atoms have been omitted and only those atoms comprising the hexagonal units have been labelled. Click image or here for a 3D representation.1C131H145N15Ni5O37 2790.21 193(2) 0.71073 Deep blue Rectangular block 0.50×0.45×0.40 Monoclinic C2/c (no. 15) 47.428(9) 19.695(2) 17.513(3) 90 100.21(2) 90 16100(4) 21.151 0.644 44.88 10298/18/828 0.0912 {0.1941} 0.2347 {0.2785} 0.795Fig. 2 A single hexagonal unit composed of six btc anions and six nickel cations. Coordination about the octahedral nickel cations is completed by three pyridine and one water molecule. Click image or here for a 3D representation. Fig. 3 Part of an infinite ribbon. Pyridine ligands have been omitted for clarity.Note the ribbon is a single hexagon in width. Note also the alternation between bidentate and tridentate btc. Click image or here for a 3D representation.Ribbons are stacked perpendicular to b, the mean interribbon distance being 7.53(1) Å. Successive layers are displaced by 11.33 Å in the ac plane to generate ABC type stacking of the ribbons (Fig. 4). Within these infinite stacks centres of hexagons and btc units are juxtaposed in successive layers, removing the possibility of channels parallel to the stacking direction. It is useful to visualise these ribbons of edge-shared hexagons as though they were part of an infinite honeycomb layer. Adjacent imaginary honeycomb layers would be displaced to generate an ABC stacking as found in b(rhombohedral) graphite.This is illustrated in Fig. 5. This pseudo-ABC stacking facilitates a large number of weak C–H···O interactions between the axial pyridine and free oxygen of a carboxylate in a neighbouring layer within the same stack. Each hexagon forms twelve such hydrogen bonds to the next layer. Details of these interactions are given in Table 2. It is these weak hydrogen bonds which are responsible for organising the ribbons together into stacks. Fig. 4 Three ribbons that form part of an infinite stack. The view shown, the ac plane, is perpendicular to the length of the infinite ribbons i.e. down the length of the ribbon. Table 2 Inter-ribbon C–H···O distancesa d(H...A)/Å d(D–H)/Å A···H–C O2···H62_$1 0.93 O2···H63_$1 0.93 O4···H27_$2 0.93 O4···H28_$2 0.93 O5···H73_$3 0.93 O5···H74_$3 0.93 O8···H32_$4 0.93 O8···H33_$4 0.93 O11···H43_$5 0.93 O11···H44_$5 0.93 3.12 2.67 2.92 2.66 2.88 2.85 3.14 2.69 2.57 3.05 a Symmetry transformations used to generate equivalent atoms: $1 = x, 2 – y, 1/2 + z; $2 = x, 1 – y, 1/2 + z; $3 = –x, 1 – y, –z; $4 = x, 1 – y, –1/2 – z; $5 x, 2 – y, –1/2 + z.Hydrogen atoms are bonded to carbon atoms with same number. For example H62_$1 is bonded to C62_$1. Fig. 5 Pictorial representation of the ABC stacking of ribbons. Note that were Ribbon 1 extended to form an infinite honeycomb sheet, it would lie directly below Ribbon 4. There is slight interdigitation of neighbouring stacks which are held together by two hydrogen bonding interactions (see Fig.6). Four molecules of butan-1-ol are found hydrogen bonding to the ribbons. One butan-1-ol molecule is abnormally well resolved crystallographically; hydrogen atoms can be located from the difference Fourier. This molecule is involved in holding together different stacks of ribbons within the structure. It is located between stacks of ribbons and forms two hydrogen bonds: one to the nonbonding oxygen of a carboxylate (donor) and the other to a free carboxylic acid (acceptor) (Fig. 7). In addition to the hydrogen bonding of the carboxylic acid unit holding stacks of ribbons together, there is evidence for C– H(pyridine)···O (carboxylate) bonding between stacks of ribbons. The distance H24···O2 is 2.35(1) Å, suggesting a moderately strong C–H···O interaction.27 The formation of the three-dimensional structure within the compound from two types of hydrogen bonds is shown in Scheme 1.Fig. 6 View of the ac plane showing three adjacent infinite stacks of ribbons. The extent of the different stacks is suggested with dashed lines. The region between ribbons which has been circled is expanded in Fig. 7. d(D...A)/Å �(DHA)/° 115.3 135.3 118.6 130.3 124.6 125.4 115.8 137.1 135.9 114.5 3.62 (2) 3.39 (2) 3.47 (2) 3.34 (2) 3.50 (3) 3.47 (2) 3.64 (2) 3.43 (2) 3.30 (2) 3.53 (2)Fig. 7 Inter-stack hydrogen bonding. Butan-1-ol forms two hydrogen bonds—one as a donor to carboxylate, one as an acceptor from a carboxylic acid.Note also the C–H···O hydrogen bond. Hydrogen atoms have been omitted from the butan-1-ol molecule for clarity. Click image or here for a 3D representation. Scheme 1 A representation of the generation of the threedimensional structure of 1. The crystallographically well resolved molecule of butan-1- ol is located such that the two terminal atoms of the alkyl chain lie directly between a pair of btc aromatic rings in adjacent ribbons of the same stack which are 7.52 Å apart. The alkyl chain is localised by C–H···p interactions between the butan-1-ol and the btc aromatic rings. (Fig. 8) Therefore this interaction is also important in stabilising the stacking of ribbons. The mean carbon–centroid distances are 3.86(1) Å for both C93 (terminal carbon) and C92 (penultimate carbon).Shortest H···C(aromatic ring) distances are 3.05 and 3.00(1) Å, for C93 and for C92 they are 2.98 and 3.01(1) Å. C–H···centroid distance and angles are given in Table 3. These lengths are in good agreement Table 3 C–H···p distances for butan-1-ol located between two aromatic rings Hydrogen Carbon D/Å q/° (C···centroid) (H···centroid) (�C–H···centroid) 3.89 (2) 3.73 (2) 3.81 (2) 3.99 (2) H92A H93C H92B H93A C92 C93 C92 C93 with similar interactions reported in the literature.28 The remaining three molecules of butan-1-ol are hydrogen bonded to free oxygen atoms of the carboxylates and these are much less well resolved, their alkyl chains displaying large thermal motions.Fig. 8 C–H···p interactions are responsible for localising the alkyl chain of one of the butan-1-ol molecules. The butan-1-ol molecule is the same as that shown in Fig. 7. Centroid···H–C distances are 3.40 Å (H92A), 3.00 Å (H93C), 3.18 Å (H92B), 3.38 Å (H93A). Click image or here for a 3D representation. Use of the program PLATON,29 summing voxels more than 1.2 Å away from the framework, reveals that within the structure there is approximately 40% solvent accessible volume. Despite the seemingly close packing within the structure there is considerable void volume. This is due to channels that run parallel with c which comprise 33.5% of the crystal volume (5393 Å3) centred on (0,0) and (1/2,1/2) in the ab plane (Fig.9). These channels are flattened cylindrical in shape, being approximately 5 × 10 Å (atom to atom distances) in cross section. Closest Van der Waals contacts which define the perimeters of these channels are 3.1 Å (H52–H52) and 7.9 Å (O15–O15). The chemical analysis, crystallographic and TGA data suggest that these regions are filled with pyridine, butan-1-ol and water, which are highly disordered, leading to the high d/Å 115.9 136.0 123.9 123.0 3.40 (2) 3.00 (2) 3.18 (2) 3.38 (2)crystallographic R-factors. Other much smaller cavities of ca. 133 Å3 exist within the structure, which are suitable to contain water molecules suggested by TGA and chemical analysis. Liberation of the pore solvent at 150 °C results in framework collapse and X-ray powder diffraction shows the product to be amorphous.Fig. 9 View of 1 down c. At the centre of the diagram (1/2,1/2) is located one of the substantial pores within the structure. Discussion It is a curious feature of the phase presented here that an excess of pyridine leads to ribbons rather than ABC stacked hexagonal sheets as might be expected. The use of 2- methylbutan-1-ol as solvent gives a phase templated by pyridine with honeycomb sheets, in which ABC stacking facilitates a large number of C–H(pyridine)···O interactions and also allows binding of free pyridine through C–H···p interactions.22 The greater propensity of butan-1-ol to engage in hydrogen bonding is clearly a more important structure directing effect in the present case.The presence of an excess of pyridine in the reaction mixture and consequent binding of three molecules of pyridine to each nickel is important in determining the local geometry about nickel. The coordination about nickel is completed by a water molecule in preference to butan-1-ol because water can form two hydrogen bonds to carboxylates rather than one. These two hydrogen bonds formed by water lock the two trans btc units in the same plane which enforces the planar geometry of the ribbons. As in analogous phases,22 weakdash;H···O hydrogen bonds are important in determining the stacking of honeycomb sheets. Slight puckering of ribbons, resulting in tilting of some of the axial pyridine molecules, and the pseudo-ABC stacking are responsible for maximising these interactions between layers so that each axial pyridine forms one short and one longer hydrogen bond to a carboxylate in an adjacent layer.Another striking feature is the presence of a carboxylic acid which is still protonated, despite the use of excess base. There is clear evidence for this protonation: the two C–O distances for the acid are 1.214(13) and 1.313(14) Å. This acid is engaged in hydrogen bonding to butan-1-ol which is one of the interactions responsible for holding together neighbouring stacks of ribbons. The additional energy gained through this hydrogen bonding between stacks must be sufficient to ensure that deprotonation does not occur. Butan-1-ol located between two aromatic rings is tightly held by two pairs of C–H···p interactions. This aliphatic C– H···p interaction is comparatively rare.The alkyl chain displays only limited thermal motion despite the nonbonded nature of its interaction with the framework. The absence of disorder and proximity of the butan-1-ol alkyl chain to the aromatic systems strongly suggest that the alkyl chain is localised by this interaction. References 1 (a) J. C. Bailar, Jr., in Preparative Inorganic Reactions, ed. W. L. Jolly, Interscience, New York, 1964, vol. 1, pp. 1–25; (b) B. F. Hoskins and R. Robson, J. Am. Chem. Soc., 1990, 112, 1546. 2 O. M. Yaghi, H. L. Li, C. Davis, D. Richardson and T. L. Groy, Acc. Chem. Res., 1998, 31, 474. 3 T. J. Barton, L. M. Bull, W.G. Klemperer, D. A. Loy, B. McEnaney, M. Misono, P. A. Monson, G. Pez, G. W. Scherer, J. C. Vartuli and O. M. Yaghi, Chem. Mater., 1999, 11, 2633. 4 A. F. Wells, Three-Dimensional Nets and Polyhedra, Wiley Interscience, New York, 1997. 5 (a) D. J. Chesnut and J. Zubieta, Chem. Commun., 1998, 1707; (b) R. J. Williams, A. C. Larson and D. T. Cromer, Acta Crystallogr., Sect. B, 1972, B28, 858; (c) D. T. Cromer and A. C. Larson, Acta Crystallogr., 1962, 15, 397; (d) B. F. Abrahams, B. F. Hoskins, J. Liu and R. Robson, J. Am. Chem. Soc., 1991, 113, 3045; (e) B. F. Abrahams, B. F. Hoskins and R. Robson, J. Chem. Soc., Chem. Commun., 1990, 60. 6 (a) M. Hong, W. Su, R. Cao, M. Fujita and J. Lu, Chem. Eur. J., 2000, 6(3), 427; (b) L. R. MacGillivray, S.Subramanian, M. J. Zaworotko, J. Chem. Soc., Chem. Commun., 1994, 1325; (c) S. R. Batten, B. F. Hoskins and R. Robson, New J. Chem., 1998, 173; (d) S. R. Batten, B. F. Hoskins, B. Moubaraki, K. S. Murray and R. Robson, Chem. Commun., 2000, 1095. 7 M. Bertelli, L. Carlucci, G. Ciani, D. J. Prosperpio and A. Sironi, J. Mater. Chem., 1997, 7, 1271. 8 D. J. Duchamp and R. E. Marsh, Acta Crystallogr., Sect. B, 1969, B25, 5. 9 D. J. Plaut, K. M. Lund and M. D. Ward, Chem. Commun., 2000, 769. 10 M. J. Plater, M. R. S. J. Foreman, E. Coronado, C. J. Gómez-García and M. Z. Slawin, J. Chem. Soc., Dalton Trans., 1999, 4209. 11 M. R. S. J. Foreman, T. Gelbrich, M. B. Hursthouse and M. J. Plater, Inorg. Chem, Commun., 2000, 3(5), 234. 12 M.J. Plater, A. J. Roberts, J. Marr, E. E. Lachowski and R. A. Howie, J. Chem. Soc., Dalton Trans., 1998, 797. 13 A. Michaelides, S. Skoulika, V. Kiritsis, C. Raptopoulou and A. Terzis, J. Chem. Res., 1997, (S) 204; (M 1344. 14 S. S.-Y. Chui, A. Siu and I. D. Williams, Acta Crystallogr., Sect. C, 1999, C55, 194. 15 O. M. Yaghi, H. Li and T. L. Groy, J. Am. Chem. Soc., 1996, 118, 9096. 16 H. J. Choi, T. S. Lee and M. P. Suh, Angew. Chem. Int. Ed., 1999, 38, 1405.17 H.J. Choi and M.P Suh, J. Am. Chem. Soc., 1998, 120, 10622. 18 O. M. Yaghi, G. Li and H. Li, Nature, 1995, 378, 703. 19 S.-Y. Chui, S. M.-F. Lo, J. P. H Charmant, A. G. Orpen and I. D. Williams, Science, 1999, 283, 1148. 20 O. M. Yaghi, C. E. Davis, G. Li and H. Li, J. Am. Chem. Soc., 1997, 119, 2861. 21 C. J. Kepert and M. J. Rosseinsky, Chem. Commun., 1998, 31. 22 C. J. Kepert, T. J. Prior and M. J. Rosseinsky, J. Solid State Chem., 2000, 152, 261. 23 C. J. Kepert, T. J. Prior and M. J. Rosseinsky, J. Am. Chem. Soc., 2000, 122, 5158. 24 G. M. Sheldrick, SHELXS-86, Universität Göttingen, 1986. 25 G. M. Sheldrick, SHELXL-97 Program for the refinement of crystal structures, Universität Göttingen, 26 L. J. Farrugia, ORTEP-3 FOR WINDOWS, J. Appl. 1997. Crystallogr., 1997, 30, 565. 27 J. Berstein, R. R. Davis, L. Shimon and N.-L. Chang, Angew. Chem., Int. Ed. Engl., 1995, 1555. 28 L. N. N. Madhavi, A. K. Katz, H. L. Carrell, A. Nangia and G. R. Desiraju, Chem. Commun., 1997, 1953 and references therein. 29 A. L. Spek, Acta Crystallogr., Sect. A, 1990, A46, C34. † The 4th century mathematician Pappus, in Book V (On the Sagacity of Bees) of his Synagoge, introduces what has become known as The Honeycomb Conjecture: "There being, then, three figures which of themselves can fill up space round a point, viz. the triangle, the square and the hexagon, the bees have wisely selected for their structure that which contains most angles, suspecting indeed that it could hold more honey than either of the other two." This conjecture has recently been shown to be true by Thomas C. Hales, University of Michigan. (http://www.math.lsa.umich.edu/~hales/) CrystEngComm © The Royal Society of Chemistry 2000