FT-IR INVESTIGATION OF POLARIZABLE, STRONG HYDROGEN-BONDS IN SULFONIC-ACID-SULFOXIDE, SULFONIC-ACID-PHOSPHINE-OXIDE, AND SULFONIC-ACID-ARSINE-OXIDE COMPLEXES IN THE MIDDLE-INFRARED AND FAR-INFRARED REGION

Ten 1:1 methanesulfonic acid-oxide systems are studied in acetonitrile-chloroform (2:1) solutions in the middle-infrared (MIR) and far-infrared (FIR) regions at 20 and -40 degrees C as a function of the basicity of the oxide. An IR continuum demonstrates that first a proton potential with a relatively narrow single minimum at the acid is present. This minimum shifts with increasing basicity in the direction of the oxide and becomes much broader. The proton polarizability is largest with the most symmetrical systems. With a further increase of the basicity, the minimum approaches the base and becomes narrow again. This shift is studied considering the SO stretching vibration bands. Furthermore, it is concluded from the splitting of these bands with increasing polarity of the complexes that these complexes associate via dipole-dipole forces. This is confirmed by osmometric measurements. The observed hydrogen bond vibrations differ largely from hydrogen bond stretching vibrations, nu(sigma), and have very difficult vibration character. With the asymmetrical systems the bands of the hydrogen bond vibrations are relatively narrow. With the more or less symmetrical systems the continua, caused by the hydrogen bonds with large proton polarizabilities, extend in the FIR region and the hydrogen bond vibration broadens extremely. This broadening effect of the hydrogen bond vibration should be explained by theoretical studies.