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)

Abstract

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) Å, β=110.51(3)°, 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) Å and Z=4. In the 1:1 complex a symmetrical [N⋯H⋯N] + hydrogen bond of length 2.579(2) Å is formed, whereas in the 1:2 complex both [N–H⋯N] + and [N–H⋯N] − bridges (2.581(3) and 2.688(3) Å) 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 ν s(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. © 1997 Elsevier Science B.V.