The structure and IR spectra of the 1:1 and 1:2 adducts of 1,8-bis(dimethylamino)naphthalene (DMAN) with 4,5-dicyanoimidazole (DCI)

Crystals of the 1:1 and 1:2 adducts of 1,8-bis(dimethylamino)naphthalene (DMAN) with 4,5-dicyanoimidazole (DCI) were grown, and were studied by using X-ray diffraction and IR spectrometry. The DMAN.DCI complex crystallizes in space group P2(1)/m, with a = 7.999(3), b = 11.566(2) and c = 10.706(4) Angstrom, beta = 110.51(3)degrees and Z = 2, whereas DMAN.(DCI)(2) crystallizes in space group Pbcm with a = 9.931(1), b = 34.895(3) and c = 7.055(1) Angstrom and Z = 4. In the 1:1 complex a symmetrical [N...H...N](+) hydrogen bond of length 2.579(2) Angstrom is formed, whereas in the 1:2 complex both [N-H...N](+) and [N-H...N](-) bridges (2.581(3) and 2.688(3) Angstrom) are asymmetric. An extended equalization of the charge distribution in the two moieties of the homoconjugated anion is visible. The asymmetry of the [NHN](+) bridge is very well reflected in the position of the v(5)(NHN) stretching vibration band, which is markedly shifted to higher frequencies as compared with the symmetric bridge. The IR behaviour of the [NHN](-) bridge is similar to that of other strongly asymmetric homoconjugated cations and anions. (C) 1997 Elsevier Science B.V.