AN INFRA-RED SPECTROSCOPIC STUDY OF GAS PHASE HYDROGEN-BONDED COMPLEXES OF FORMULA (HCN)2 AND NH3 HCN

Three parallel bands have been observed for each of the gas phase complexes H3N⋯HCN and D3N⋯DCN corresponding to the fundamental C-H(C-D) and CN stretching and the symmetric NH3(ND3) deformation vibrations. The band contour of the CN stretching vibration in H3N⋯HCN is of the form expected for a symmetric-top molecule and yields a lower limit of 3·0 Å for the N....C distance. An analogous band in the spectrum of (HCN)2 gives a similar value of about 3·3 Å for the N....C distance in the dimer. Reasons are put forward for the non-observance of perpendicular infra-red bands from these complexes. Some anomalous structure on the 3160 cm-1 bond of the H3N⋯HCN complex is discussed. Attempts to obtain infra-red spectra from complexes of formula H3N⋯HCl and H3P⋯HI were unsuccessful. © 1969.