Intermolecular interactions investigation of nickel(II) and zinc(II) salts of ortho-sulfobenzoic acid by X-ray diffraction and vibrational spectra

Two isostructural compounds consisting of hexaaquanickel(II) or hexaaquazinc(II) cations and hydrogen ortho-sulfobenzoate (HSBZ) as counter-ions have been synthesized and characterized by X-ray diffraction and vibrational spectroscopy techniques. The metal atom is located in the inversion centre and has a slightly distorted octahedral environment formed by water molecules, giving rise to ionic compounds with HSBZ. The HSBZ ions which are related by a c-glide plane interact to each other by medium to weak hydrogen bonds, developing wave-like chains parallel to the crystallographic c-axis. The [M(H2O)6]2+ cation interacts with six surrounding HSB via the coordinated water molecules by hydrogen bonds. The oppositely charged units are interconnected into a 2D-polymeric superstructure parallel to (1 0 0) plane. The vibrational spectra of both salts are very similar to ortho-sulfobenzoic acid spectrum, and no significant shifts in SO and CO stretching bands were observed, suggesting the formation of ionic salts, which is in agreement with the X-ray results, thus indicating that the ortho-sulfobenzoate anion is a weaker ligand than water. Moreover, the presence of the acidic structure is very important in the definition of the supramolecular structure, since the hydrogen bonds design of the HSBZ is related to the cation size, probably due to the spatial factors involved in the crystal packing stability.