Vibrational study of strong CH · middot; X hydrogen bonds in solid complexes of boron decachlorocarboranes

Abstract Solid complexes of boron decachloro- o -carborane and boron decachloro- m -carborane (B 10 Cl 10 C 2 H 2 ) with some oxygen and nitrogen bases have been investigated by infrared and Raman spectroscopy. Complexes containing CH · · O hydrogen bonds are characterized by a relative CH stretching frequency shift up to 12% and a halfwidth of the νCH band up to 220 cm −1 . CH · · N hydrogen bonds, with trimethylamine for example, are stronger with a relative shift of about 18% and ν 1 2 of about 500 cm −1 . Triethylamine complexes, however, form a NH + · · C − proton transfer hydrogen bond while pyridine can give either CH · · N or C − · · + HN hydrogen-bonded adducts depending on the solvent and temperature. The CH · · N↔c − · · + HN equilibrium appears to be shifted towards ion-pair formation at considerably smaller enthalpy values compared to the OH · · N↔O − · · + HN system. CH and NH stretching frequencies are correlated with the acidity of the donor and the basicity of acceptor molecules.