Dimorphism of Hexaaquanickel(Ii) Bis(p-Nitrobenzoate) Dihydrate Salt: A New Triclinic Crystal Form

Room temperature crystallization from a water/ethanol solution of NiSO4, p-nitrobenzoic acid (HPNBA), and thiourea yields single crystals of [Ni(H2O)6](PNBA)2·2H2O. Crystal data are: a = 5.9626(8), b = 7.3552(11), c = 12.3459(17) A, α = 97.885(12), β = 96.714(11), γ = 91.158(11)°, V = 532.28(13) A3, space group Pī, Z = 1. An alternative monoclinic crystal form of the same compound with a slightly lower packing efficiency was previously obtained. The Ni(II) cation is located on a crystallographic inversion center and octahedrally coordinated by six water molecules. The PNBA moieties occupy an outer coordination sphere acting as counter-anions. An intricate system of H bonds between the complex cation, the PNBA anions, and the co-crystallized water molecules results in a three-dimensional network.