Reversible Dissociation of (Se₆I₂)(AsF₆)₂ in SO₂(I)

Abstract

The dissociation of (Se₆I₂)(AsF₆)₂ in SO₂(1) has been investigated by ⁷⁷Se NMR spectroscopy at –80 °C involving both a natural-abundance sample as well as that containing selenium enriched in the ⁷⁷Se-isotope (enrichment 92 %). In addition to the previously characterized cations Se₆I₂ ²⁺, SeI₃ ⁺, 1,1,4,4-Se₄I₄ ²⁺, Se₁₀ ²⁺, Se₈ ²⁺, and Se₄ ²⁺, the NMR spectra of the equilibrium solution exhibited additional resonances the assignment of which has been carried out by ⁷⁷Se-⁷⁷Se COSY, selective irradiation experiments, and spectral simulation. Combining this information with the trends in the chemical shifts as well as with iodine, selenium, and charge balances that were calculated from quantitative integrated intensities, the presence of cyclic cations Se₇[⁺ and 1,4-Se₇I₂ ²⁺, as well as acyclic Se₂I⁺, and 1,1,6,6-Se₆I₄ ²⁺(two rotamers) could be inferred. Upon evaporation of the solvent only Se₆I_2²⁺ was found to be present in the solid state.

Keywords::

• Selenium-iodine cations
• ⁷⁷Se NMR spectroscopy