77Se NMR Spectroscopic, DFT MO, and VBT Investigations of the Reversible Dissociation of Solid (Se6I2)[AsF6]2•2SO2 in Liquid SO2 to Solutions Containing 1,4-Se6I22+ in Equilibrium with Sen2+ (n = 4, 8, 10) and Seven Binary Selenium Iodine Cations: Preliminary Evidence for 1,1,4,4-Se4Br42+ and cyclo-Se7Br+

The composition of a complex equilibrium mixture formed upon dissolution of (Se6I2)[AsF6]2·2SO2 in SO2(l) was studied by 77Se NMR spectroscopy at −70 °C with both natural-abundance and enriched 77Se-isotope samples (enrichment 92%). Both the natural-abundance and enriched NMR spectra showed the presence of previously known cations 1,4-Se6I22+, SeI3+, 1,1,4,4-Se4I42+, Se102+, Se82+, and Se42+. The structure and bonding in 1,4-Se6I22+ and 1,1,4,4-Se4I42+ were explored using DFT calculations. It was shown that the observed Se−Se bond alternation and presence of thermodynamically stable 4pπ−4pπ Se−Se and 4pπ−5pπ Se−I bonds arise from positive charge delocalization from the formally positively c…