2-Amino-benzoxazole-oxalic acid (2/1).

In the title compound, 2C7H7N2O+·C2O4 2-, proton transfer from oxalic acid to the N atom of the heterocycle has occurred to form a 2:1 molecular salt. In the extended structure, N-H⋯O hydrogen bonds link the components into [100] chains, which feature R 2 2(8) and R 4 4(14) loops.

Synthesis, crystal structure and Hirshfeld surface analysis of hexa-aqua-nickel(II) bis-(4-hy-droxy-benzoate) dihydrate.

The title compound, [Ni(H2O)6](PHB)2·2H2O (1) (PHB = 4-hy-droxy-benzoate, C7H5O3), was obtained by the reaction of NiCl2, 4-hy-droxy-benzoic acid (PHBA) and mono-ethano-lamine in aqueous ethanol solution. The NiII ion is coordinated by six water mol-ecules and is located on an inversion center. The outer coordination sphere in the asymmetric unit comprises one PHB anion and one water mol-ecule, i.e. the compound is a salt and a hydrate consisting of three components. In the crystal, the components are packed into an inter-molecular network stabilized by O-H⋯O hydrogen bonds. A comprehensive Hirshfeld surface analysis was carried out to investigate the inter-molecular inter-actions in detail.