Homoatomic Sulfur Cations
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This chapter gives an account on the recent achievements in an understanding of the synthesis, solution behavior, structure and bonding of the homopolyatomic sulfur cations. A focus is put on the developments aimed to understand experimental observations, i.e., quantum chemical calculations of these electronically delicate species. The synthesis of the highly electrophilic sulfur cations requires the use of very weakly basic conditions throughout, that is weakly coordinating counterions such as AsF6 −, SbF6 −, Sb2F11 − as well as weakly basic solvents such as SO2, HF, HSO3F. Structure and bonding of the currently structurally characterized S4 2+, S8 2+, and S19 2+ cations are governed by positive charge delocalization brought about by 3pπ-3pπ, π*-π* and 3p2→3σ* bonding interactions. The solution behavior of S8 2+ salts, which give rise to several sulfur radical cations such as S5 ·+, was analyzed in detail based on (calculated) thermodynamic as well as spectroscopic considerations and hitherto unknown D 3d symmetric S6 2+ and D 4h symmetric S4 ·+ are likely players in SO2 solutions of S8(AsF6)2.
KeywordsSulfur Cation Ab initio Bonding DFT
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