Structure and energy calculations for imide and methide anions containing perfluoroalkanesulfonyl groups

Abstract

The calculated potential energy maps for rotation about the S–C–C–S dihedral in the isolated anions N(CF3SO2)2−, N(CF3CF2SO2)2−, N(CF3SO2)(CF3(CF2)3SO2)− show only small energy barriers for rotation. Three stabilizing factors are identified: a staggered orientation for groups bound to the sulfurs, close interaction of fluoroalkane groups where possible and a high charge separation for S, N and O atoms. Ab initio Hartree–Fock (HF) and density functional theory (DFT) calculations for these anions and C(CF3SO2)3− provide structures and relative energies for optimized conformations, these are compared with experimental crystallographic data where available.