The totally symmetric Raman stretching vibration (ν)over-tilde(Mo-Mo) of quadruple molybdenum-molybdenum bonds varies linearly with the mass of molybdenum and its ligands

The electronic (400-800 nm), i.r. and Raman (20-400 cm(-1)) spectra of several hexahalo-di(aquo)dimolybdate(II) anions, Mo2X6(H2O)(2)(2-) (X = Cl, Cl/Br, Br and I) containing quadruple metal-metal bonds have been investigated. The electronic spectra of the solid compounds at 300 K show intense bands in the visible region (510-580 nm) assigned to the expected delta --> delta* transitions. From the i.r. and Raman spectra the skeletal and stretching modes in these binuclear anions have been identified. The metal-metal <(nu)over tilde>(Mo-Mo) stretching vibrational wavenumbers vary linearly. as a function of the total mass, including molybdenum and its ligands. From this relationship, the mass of the ligands and that of the unknown material have been determined and compared with analytical results. In conclusion, the results are in very good agreement.