Hydrothermal Synthesis of Co(pdc)  2H 2 O (pdc  3,5-Pyridinedicarboxylate). A Two-dimensional Coordination Polymer M. John Plater,* Alexander J. Roberts and R. Alan Howie Department of Chemistry, Aberdeen University, Meston Walk, Aberdeen AB24 3UE, UK A hydrated coordination polymer is formed by heating the tecton 3,5-pyridinedicarboxylic acid (H 2 pdc) with cobalt(II) acetate. Metal-ion directed assembly of organic molecular building blocks known as tectons is giving access to new open frame- work solid-state materials with fascinating technological potential and scienti®c interest. 1 Supramolecular chemistry has frequently centered on the synthesis of hosts with convergent functional groups to form binding cavities which mimic enzyme active sites and can show homogeneous catalytic activity. 2 The synthesis of 1D, 2D and 3D coordination polymers, which are structurally analogous to important minerals such as quartz and zeolites, 3 and have the potential for heterogeneous catalysis, requires rigid tectons which possess divergent functional groups. Methods for the assembly of crystalline lattices from organic tectons and metal ions which may show stability to guest or template desorption/adsorption are of considerable current interest. Here we report the hydrothermal synthesis and X-ray single-crystal structure characterisation of Co(pdc)  H 2 O. 3,5-Pyridinedicarboxylic acid (100 mg) and a stoichiometric quantity of Co(OAc) 2  4H 2 O in water (10 ml) were heated to 180 8C and allowed to cool slowly. Pink crystals of Co(pdc)2H 2 O were obtained in 90% yield which are insoluble in boiling water. Hydrothermal synthesis is essential to obtain good quality crystals. If the same quantities of reagents are re¯uxed in water (200 ml) for 2 h complete dissolution does not occur but a pink microcrystal- line material identical with the above material does slowly form. The structure shown in Fig. 1 consists of in®nite layers of alternating Co II cations and 3,5-pyridinedicarboxy- late dianions. Each cobalt ion is seven-coordinate and is coordinated by two identical bidentate carboxylate groups, one pyridine nitrogen and two water molecules. The Co II ions coordinate to the pdc tectons along the crystallographic a axis with Co0O(1) and Co0O(2) bond lengths of 2.157(4) and 2.432(4) A Ê respectively. Although the Co0O(2) bond length is quite long it is shorter than the estimated cobalt±oxygen van der Waals distance of 2.562 A Ê . This is calculated as the sum of the Co single bond metallic radius of 1.161 A Ê and the van der Waals radius of an oxygen atom of 1.400 A Ê . 5 The carboxylate anions form a dihedral angle of 13.3(7)8 to the pyridine ring. The pyridine nitrogens coordinate to each cobalt ion along the crystallographic b axis forming a Co0N distance of 2.206(7) A Ê . Hence in the ab plane the structure consists of a 2D coordination polymer. The layers are not chemically bonded together in the c axis direction but are interleaved with water molecules coordinated to each cobalt ion with a cobalt±oxygen bond length of 2.072(4) A Ê . The hydrogen atoms of the water molecules form interlayer hydrogen bonds to the carboxylate groups. Adjacent 2D layers are related by crystallographic centres of symmetry with parallel pyridine rings stacked 3.7 A Ê apart in a zigzag arrangement almost on top of each other along the c axis. The zigzag arrangement of pyridine rings occurs parallel to the b axis. The half thickness of an aromatic ring is 1.85 A Ê 6 so the pyridine rings are stacked at the optimum van der Waals distance. The layers are neutral, interleaved with water molecules and might be easily cleaved apart. In this respect the compound J. Chem. Research (S), 1998, 240±241 J. Chem. Research (M), 1998, 1001±1013 Fig. 1 A view down c of the cation/anion layer with z/c close to 1/4 for all atoms shown. The water molecules and hydrogen atoms have been omitted for clarity. Atoms are shown as 40% probability elipsoids Fig. 2 The coordination of Co. Atoms are shown as 40% probability ellipsoids *To receive any correspondence (e-mail: m.j.plater@abdn.ac.uk). 240 J. CHEM. RESEARCH (S), 1998 Published on 01 January 1998. Downloaded on 25/10/2014 12:04:33. View Article Online / Journal Homepage / Table of Contents for this issue