We report herein the single crystal structures of four metal-organic framework complexes incorporating the 4,4'-dicarboxy-2,2'-bipyridine ligand, H(2)dcbp: alpha-[Co(dcbp)(H(2)O)(2)], 1; beta-[Co(dcbp)(H(2)O)(2)], 2, [Ni(dcbp)(H(2)O)(2)], and [[Mn(dcbp)].1/2DEF], 4 (DEF = diethylformamide). In each complex the ligand is deprotonated giving neutral species with 1:1 stoichiometry that form three-dimensional coordination polymers. Supramolecular isomerism (polymorphism) in 1 and 2 arises from the different ligand connectivity around the octahedral Co(II) centres. The two coordinated water molecules in 1 occupy cis positions, which are trans to the chelating bipyridine nitrogen atoms, leaving the carboxylate oxygen atoms in axial trans positions. In 2 all like donors occupy cis positions. Different modes of carboxylate coordination in 1 and 2 give dissimilar network topologies. A rare example of two interpenetrating 6(4)8(2)-b (quartz-like) chiral networks in 1 results from both dcbp carboxylate groups coordinating in a monodentate fashion to adjacent Co(II) centres, whereas in 2 only one carboxylate group bridges between adjacent Co(II) centres giving rise to a single chiral (10,3)-a net. In 1 and 2 the coordinated water molecules hydrogen bond to the non-coordinated carboxylate oxygen atoms. These interactions give rise to water-carboxylate double helices in , and support the coordination network in 2. Strikingly for a pair of dimorphs the crystal densities of 1 and 2 differ by ca. 0.3 g cm(-3)(1.654 vs. 1.940 g cm(-3), respectively). Compound 3 is isomorphous with 1 and likewise features two chiral interpenetrating nets of quartz topology. In 4, chelating bipyridine nitrogen atoms and four carboxylate oxygen atoms from a total of five adjacent dcbp ligands provide distorted octahedral geometry around Mn(II). The carboxylate groups bridge adjacent Mn(II) centres to produce bis-carboxylato chains which cross-link and generate a 3D network that is perforated with channels. The channels are occupied with disordered DEF molecules. The network topology in 4 is quite different to 1-3 and has a (4.6(2))(4(2).6)(4(3).6(6).8(6)) Schlafli notation. Magnetic susceptibility studies performed on 1, 2, [[Mn(dcbp)].1/2DMF] 5 (DMF = dimethylformamide) and [[Mn(dcbp)].2H(2)O] 6 reveal very weak antiferromagnetic coupling between the metal centres in each case.

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Reported herein is a synthetic and structural study of the coordination chemistry of 4,4 0 ,6,6 0tetracarboxylic acid-2,2 0 -bipyridine (H 4 tcbp) with some lanthanide ions. The reaction of H 4 tcbp under acidic hydrothermal conditions with Ln(III) (Ln ¼ La, Eu and Gd) in 1 : 1 stoichiometric ratio led to the formation of crystalline {, 4; which were structurally characterised. Using a 1 : 1 H 2 O/DMF-solution in combination with Eu(III) and H 4 tcbp gave {[Eu(tcbp)(H 2 O)]$(Me 2 NH 2 )}, 5, which was also structurally characterised. The acidic conditions in 1-4 yielded 1 : 1 neutral {Ln : Htcbp} complexes whereas in 5 the H 4 tcbp ligand is fully deprotonated and charge neutrality is brought about by the presence of a dimethylammonium cation (arising through the hydrolysis of the DMF solvent). Complex 1 forms a 1D coordination polymer which cross-links through extensive hydrogen bonding to form a complicated 3D network. Each {Ln(Htcbp)} moiety in 2 acts as a four-connecting node and forms a 2D sheet with (4,4)-topology, which is different to the 2D sheets with (4,4)-topology formed in isostructural 3 and 4. Within 5 each [Eu(tcbp)] À moiety acts as a 5-connecting node forming a heretofore unprecedented 2D 5-connected network with (3 3 .4 3 .5 4 ) topology. Furthermore, each 2D sheet in 2-5 features an array of hydrogen bonded contacts both within and between neighbouring sheets to give complicated 3D networks.

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