Fourier transform infrared studies of 1:12 and 1:11 heteropoly tungstates.

Abstract

Infrared spectroscopic features of 1:12 and 1:11 heteropoly tungstates were studied using FT -IR. Internal coordinate analysis revealed that 297 coordinates are required for the 1:12 heteropoly anions, and 303 for the1: 11 an ions. The spectra of compounds of these two families were identified and characterized using 'fingerprint' and computerized search methods. For the computer searches, four spectral libraries were created for the four different dispersive media, KBr, KC1, Nujol and CC14. Major bands were assigned to specific localized vibrations. An absorbance study was performed with selected compounds using a new weighing scheme. The accuracy of this scheme was matched with the usual technique for tripalmitin in CC14 solution and was found to be simpler and more advantageous. An unusual absorbance vs concentration behavior was observed. This phenomenon is interpreted in terms of different vibrational nature of the anions at different concentration ranges. The absorbance study also indicated that for a given heteropoly compound in non-polar solvents, the absorption proportionality constant is also a function of concentration. Some uncertainties were observed about the stability of these compounds in the solutions with respect to time and temperature.