Crystal structure, Raman and resonance Raman spectroscopic studies of the dimethyl diquaternary salt of 2,2′-dicyano-4,4′-bipyridine and its radical monocation

Abstract

The crystal structure of the dimethyl diquaternary salt of 2,2′-dicyano-4,4′-bipyridine is reported. Crystal data: C 14H 12Br 2N 4, M r = 396.1, a = 7.1934(9), b = 10.192(1), c = 10.715(1) Å, β = 103.89(1)°, V = 762.61 Å 3, monoclinic, space group P2 1/ n, Z = 2, D m = 1.70, D c = 1.73 g cm −3, Mo Kα, λ = 0.71069 Å, μ = 56.24 cm −1, F(000) = 388, T = 293 ± 1 K, R = 0.028, R w = 0.029 for 1156 ( I > 2.50σ(I)) reflections. The cation straddles a crystallographic centre of symmetry with the two pyridine rings being coplanar. The bromide ion is in a general position. Bond lengths and angles are normal. Raman spectra of the parent dication and resonance Raman spectra of the coloured radical monocation are also reported. The CN stretching frequency for the radical monocation is only weakly enhanced and is displaced only 12 cm −1 from the corresponding feature for the parent dication.