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

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)(3)SO2)(-) 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. (C) 2000 Elsevier Science Ltd. All rights reserved.