A normal coordinate analysis of the vibrational modes of the three redox forms of methylviologen: Comparison with experimental results

Abstract

A normal coordinate analysis of the three redox forms of methylviologen (MV) was accomplished using a simplified valence force field. The calculated band frequencies are compared with those observed experimentally. The plausibility of the assignments for the Raman A g modes, as inferred from the normal coordinate analysis, is discussed. The assignments of several Raman A g modes were checked by a comparison of the observed Raman spectra of viologens with different substituents, such as methyl group deuterated methyl viologen (DV), N-octyl- N′-methyl viologen (C 8MV), N-hexadecyl- N′-methyl viologen (C 16MV) and dibenzyl viologen (BV), with MV. The values of the root mean square (r.m.s.) amplitudes of vibrations between the bonded and the nonbonded atom pairs, and r.m.s. Cartesian displacements from the equilibrium geometry for MV 2+ were computed. These data provide important insight with respect to the molecular geometry.