DENSITY-FUNCTIONAL THEORY STUDY OF TRANSITION-METAL COMPOUNDS CONTAINING METAL-METAL BONDS - 2 - MOLECULAR-STRUCTURES AND VIBRATIONAL-SPECTRA OF DINUCLEAR TETRACARBOXYLATE COMPOUNDS OF MOLYBDENUM AND RHODIUM

Vibrational spectra have been calculated for the first time for dinucl ear transition-metal compounds containing metal-metal bonds. The calcu lations were carried out by employing different forms of density funct ional theory (DFT) and basis functions of different sizes at fully opt imized molecular geometry. The calculated frequencies essentially repr oduced fundamentals observed in experimental infrared and Raman spectr a. It is shown that DFT frequency calculations can be a very important and valuable tool to assist in analyzing and assigning measured infra red and Raman spectra and to predict vibrational frequencies for large transition-metal compounds with metal-metal bonds. The molecules incl uded in this study were M-2(O2CH)(4) (M = Mo, Rh), Rh-2(O2CH)(4)(H2O)( 2), and M-2(O2CCH3)(4) (M = Mo, Rh). Significant differences are found between the formate and acetate molecules.