A density functional investigation of the structural and vibrational properties of the highly symmetric molecules M4O6, M4O10 (M = P, As, Sb, Bi)

The group 15 (VA) M4O6, M4O10 (M: N, P, As, Sb, Bi) oxides have a cage-like structure. These compounds could be found as isolated gas-phase molecules or as structural units in condensed systems. They serve as molecular ‘models’ that could describe the structure and physicochemical properties of various solid- and liquid-state systems. The knowledge of the geometric parameters (bond lengths, angles), of the atomic charges and of the bond stretching frequencies is important for the investigation and understanding of the nature of the metal–oxygen chemical bonds in these molecules.In the present work we systematically investigated by density function theoretical (DFT) methods the modification of the structure and of the vibrational spectrum of the M4O6 and M4O10 molecules at two different symmetries (Td and D2h). Computer calculations were performed at the B3LYP level of theory using the LanL2DZ (ECP) basis set. An enlargement of the metal–oxygen bond length and a shift of vibrations to lower frequencies have been observed when the metal element changes from phosphorous to bismuth, for both oxidation states and symmetries.