Sodium thiosulfonate salts: Molecular and supramolecular structural features and solution radiolytic properties

摘要

Three sodium thiosulfonate salts, NaMeS_2O_2· H_2O, NaPhS_2O_2 and NaMeC_6H _4S_2O_2 have been prepared by the direct reaction of the sodium sulfinate salts with elemental sulfur, a clean, benign route that produces no by-products. The structures of the phenyl (which crystallised as a hydrate, NaPhS_2O_2·1.5H_2O) and p-tolyl compounds were determined by X-ray crystallography. For the p-tolyl derivative, NaMeC_6H_4S_2O_2, the unexpected coordination of the pendant sulfur atom was found, a feature not reported previously for thiosulfonate salts, and observed only in two of the more common thiosulfate salts. Intermolecular CH/π interactions are postulated to contribute to the driving force of sulfur coordination, otherwise a different orientation of the aromatic rings would be expected. For NaPhS-2O _2·1.5H_2O, the water ligands and thiosulfonate anions each contribute three oxygen atoms to form a NaO_6 coordination sphere. The thiosulfonate and water oxygens bridge to other sodium atoms forming a three-dimensional layer structure consisting of sheets of NaPhS _2O_2·1.5H_2O with a hydrophilic interior layer, comprising the sodium ions, water ligands and -S_2O _2~- groups, and a hydrophobic exterior formed by the phenyl substituent. The structure is further stabilised by an extensive H-bonding network between the ligated water and the non-coordinating thiosulfonate sulfur atom forming part of the hydrophilic layer and by weak intermolecular edge-to-face CH/π interactions between the sheets. Investigation of the radical chemistry of the three salts using pulse radiolysis indicated that oxidation of NaMeS_2O_2·H_2O involves formation of a sulfur-centred radical rather than hydrogen abstraction from the methyl substituent, whereas oxidation of the aromatic ring is the preferred pathway for the phenyl and p-tolyl derivatives.