Coordination and hydrogen bonded networks featuring 4,4′-dicarboxy-2,2′-bipyridine (H2dcbp): structural characterisation of H2dcbp, [Co(dcbp)(H2O)4]·4H2O, and {[Cu(dcbp)(H2O)2]·2H2O}n

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Abstract
We report herein the single crystal structures of 4,4′-dicarboxy-2,2′-bipyridine, H2dcbp, and two complexes it forms with Co(II), [Co(dcbp)(H2O)4]·4H2O, 1, and Cu(II), {[Cu(dcbp)(H2O)2]·2H2O}n, 2. H2dcbp adopts the anti conformation in the solid-state, with a dihedral angle of 148° between each pyridyl ring. Face-to-face ππ interactions reinforce intermolecular hydrogen bonding (O–HN) involving both carboxylate oxygen and pyridyl nitrogen atoms forming a 2D inter-helical network. Alternate 2D layers are of opposite chirality and are linked into 3D through (C–HO) hydrogen bonds. In both 1 and 2 the ligand is deprotonated giving neutral complexes with 1 ∶ 1 stoichiometry. Although 1 is monomeric, extensive hydrogen bonding between the deprotonated carboxylates, lattice water, and coordinated water molecules results in a 3D network which also contains face-to-face ππ interactions between adjacent dcbp ligands. Within 2, pseudo-octahedral coordination about the Cu(II) centre is furnished by bidentate bipyridyl nitrogens, two monodentate carboxylates (from two adjacent dcbp ligands) and two water molecules. Coordination of dcbp in this instance forms a 2D coordination polymer, which is further linked by extensive hydrogen bonding between carboxylates and water molecules, giving a 3D network.

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