Density functional study of the vibrational frequencies of α-Keggin heteropolyanions

The structures and vibrational spectra of the alpha-Keggin heteropolyanions [PMo12O40](3-), [PW12O40](3-), [AsMo12O40](3-), [SiMo12O40](4-), [GeMo12O40](4-), [AlMo12O40](5-) and [GaMo12O40](5-) have been calculated using density functional theory. The calculations represent the first non-empirical study of the vibrational frequencies of this important class of polyoxometalates. The agreement between the previously reported vibrational spectra and the calculated values is, in general, good. A number of previously reported assignments have been confirmed or clarified. The calculations are extremely computationally demanding requiring precise energies and geometries and cannot presently be considered a standard task for the study of these large, heavy element cluster anions. Characteristic group frequencies for the type I polyoxometalates with isopolyanions with the Lindqvist structure and heteropolyanions with the alpha-Keggin structure have been identified and the effect of the heteroatom on these frequencies studied. The vibrational analyses confirm the high symmetry for these anions suggested by previous geometry calculations. (C) 2002 Elsevier Science B.V. All rights reserved.