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

Abstract

Abstract The structures and vibrational spectra of the α-Keggin heteropolyanions [ PMo 12 O 40 ] 3− , [ PW 12 O 40 ] 3− , [ AsMo 12 O 40 ] 3− , [ SiMo 12 O 40 ] 4− , [ GeMo 12 O 40 ] 4− , [ AlMo 12 O 40 ] 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 α-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.