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In poly[[bis(μ-4,4′-bi-1H-pyrazole-κ2N2:N2′)bis(3-carboxyadamantane-1-carboxylato-κO1)cobalt(II)] dihydrate], {[Co(C12H15O4)2(C6H6N4)2]·2H2O}n, (I), the Co2+ cation lies on an inversion centre and the 4,4′-bipyrazole (4,4′-bpz) ligands are also situated across centres of inversion. In its non-isomorphous cadmium analogue, {[Cd(C12H15O4)2(C6H6N4)2]·2H2O}n, (II), the Cd2+ cation lies on a twofold axis. In both compounds, the metal cations adopt an octahedral coordination, with four pyrazole N atoms in the equatorial plane [Co—N = 2.156 (2) and 2.162 (2) Å; Cd—N = 2.298 (2) and 2.321 (2) Å] and two axial carboxylate O atoms [Co—O = 2.1547 (18) Å and Cd—O = 2.347 (2) Å]. In both structures, interligand hydrogen bonding [N...O = 2.682 (3)–2.819 (3) Å] is essential for stabilization of the MN4O2 environment with its unusually high (for bulky adamantanecarboxylates) number of coordinated N-donor co-ligands. The compounds adopt two-dimensional coordination connectivities and exist as square-grid [M(4,4′-bpz)2]n networks accommodating monodentate carboxylate ligands. The interlayer linkage is provided by hydrogen bonds from the carboxylic acid groups via the solvent water molecules [O...O = 2.565 (3) and 2.616 (3) Å] to the carboxylate groups in the next layer [O...O = 2.717 (3)–2.841 (3) Å], thereby extending the structures in the third dimension.