Electronic effects and ring strain influences on the electron uptake by selenium-containing bonds

Abstract

The gas-phase electron attachment of thiaselena and diselena derivatives is investigated on model organic systems by ab initio calculations (level of theory MP2/DZP++). Electronic contributions favor the one-electron addition on selenium-containing compounds, with adiabatic electron affinities of 0.03, 0.24, and 0.43 eV, respectively, for dimethyldisulfide, dimethylselenenylsulfide, and dimethyldiselenide. This ensures the possibility of an excess electron, binding on - Se - S - and - Se - Se - linkages. The so-formed radical anionic intermediates present a three-electrons two-centers 2c - 3e bond, whose nature is confirmed by Mulliken spin densities and NBO analysis. They are stable towards dissociation, with a low barrier evaluated between about 25-60 kj/mol. Cyclization strongly enhances dichalcogen propensity to fix an excess electron. Adiabatic electron affinities of a series of 1,2-thiaselena-cycloalkanes and 1,2-diselena-cycloalkanes are positive and range from 0.24 to 1.30 eV. This can be traced back to the release of ring strain energy upon one-electron addition: this geometrical effect is nevertheless less marked than for disulfide analogs.