Salts of aromatic carboxylates: the crystal structures of nickel(II) and cobalt(II) 2,6-naphthalenedicarboxylate tetrahydrate

The crystal structures of isostructural 2,6-naphthalenedicarboxylate tetrahydrate salts of nickel(II) and cobalt(II) have been determined using Monte Carlo simulated annealing techniques and laboratory X-ray powder diffraction data. These compounds crystallize in the triclinic space group P 1̄, with Z = 2; a = 10.0851 (4), b = 10.9429 (5), c = 6.2639 (3) Å, α = 98.989 (2), β = 87.428 (3), γ = 108.015 (2)°, V = 649.32 (5) Å 3 for [Ni(C 12 H 6 O 4 )(H 2 O) 4 ], and a = 10.1855 (6), b = 10.8921 (6), c = 6.2908 (5) Å, α = 98.519 (4), β = 87.563 (4), γ = 108.304 (3)°, V = 655.28 (8) Å 3 for [Co(C 12 H 6 O 4 )(H 2 O) 4 ]. The water-molecule H atoms were located by quantum chemical geometry optimization using CASTEP . The structure consists of alternating hydrocarbon and metal/oxygen layers parallel to the ac plane. Each naphthalenedicarboxylate anion bridges two metal cations; each carboxyl group is monodentate. The resulting structure contains infinite chains parallel to [111]. The octahedral coordination sphere of the metal cations contains trans carboxylates and four equatorial water molecules. The carboxyl groups are rotated by 15–20° out of the naphthalene plane. The metal/oxygen layers are characterized by an extensive hydrogen-bonding network. The orientations of the carboxyl groups are determined by the formation of short (O...O = 2.53 Å) hydrogen bonds between the carbonyl O atoms and the cis water molecules. Molecular mechanics energy minimizations suggest that coordination and hydrogen-bonding interactions are most important in determining the crystal packing.