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 , 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.