Counterion and solvation effects on the conformations of the radical anions of 2,5-dicyanovinyl substituted furan and thiophene. An EPR and ENDOR study

Abstract

The radical anions of two tetranitrile compounds, i.e., 2,2′-(furan-2,5-diyldimethylidene)-bispropanedinitrile (1) and 2,2′-(thiophene-2,5-diyldimethylidene)bispropanedinitrile (2), have been investigated in a 1,2-dimethoxyethane/N,N,N′,N′,N″,N″-hexamethylphosphoric triamide mixture, 1,2-dimethoxyethane, tetrahydrofuran, and 2-methyltetrahydrofuran as the solvents and with Li⁺, Na⁺, K⁺, Cs⁺ as the counterions and in N,N-dimethylformamide with Zn²⁺ as counterion. A remarkable dependence of the molecular symmetry upon ion-pair formation is found for both molecules. The symmetry of both radical anions increases to C_2ν under conditions favouring contact ion-pair formation.