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 tetrah ydrate salts of nickel(II) and cobalt(II) have been determined using Monte Carlo simulated annealing techniques and laboratory X-ray powder diffractio n data. These compounds crystallize in the triclinic space group P (1) over bar, with Z = 2;a = 10.0851 (4), b = 10.9429 (5), c = 6.2639 (3) Angstrom, alpha = 98.989 (2), beta = 87.428 (3), gamma = 108.015 (2)degrees, V = 649 .32 (5) Angstrom (3) for [Ni(C12H6O4)(H2O)(4)], and a = 10.1855 (6), b = 10 .8921 (6), c = 6.2908 (5) Angstrom, alpha = 98.519 (4), beta = 87.563 (4),g amma = 108.304 (3)degrees, V = 655.28 (8) Angstrom (3) for [Co(C12H6O4)(H2O )(4)]. The water-molecule H atoms were located by quantum chemical geometry optimization using CASTEP. The structure consists of alternating hydrocarb on and metal/oxygen layers parallel to the ac plane. Each naphthalenedicarb oxylate anion bridges two metal cations; each carboxyl group is monodentate . The resulting structure contains infinite chains parallel to [111]. The o ctahedral coordination sphere of the metal cations contains trans carboxyla tes and four equatorial water molecules. The carboxyl groups are rotated by 15-20 degrees out of the naphthalene plane. The metal/oxygen layers are ch aracterized by an extensive hydrogen-bonding network. The orientations of t he carboxyl groups are determined by the formation of short (O . . .O = 2.5 3 Angstrom) hydrogen bonds between the carbonyl O atoms and the cis water m olecules. Molecular mechanics energy minimizations suggest that coordinatio n and hydrogen-bonding interactions are most important in determining the c rystal packing.