POLARIZED ELECTRONIC ABSORPTION-SPECTRA FOR DIMOLYBDENUM(II) TETRAACETATE

Polarized spectra with rich vibrational detail are reported for two faces of single crystals of Mo2(O2CCH3)4 at temperatures down to 5 K. Evidence, which includes the orientation in space of transition moments for individual vibrational lines, hot bands, and Franck-Condon factors, is presented that the 23000-cm-1 band is theelectric-dipole-allowed 1A2u ← 1A1g or σ* ← σ with an origin at 21700 cm-1. However, the intensities are sufficiently low that lines excited vibronically, although somewhat weaker, approach the intensity of the dipole-allowed progression. A second transition at 26500 cm-1 is evident as well from the low-temperature spectra. The spectra of a number of dimeric carboxylate complexes of molybdenum(II) are compared and the possible cause of the exceptionally low intensity for an electric-dipole-allowed transition is discussed. © 1979, American Chemical Society. All rights reserved.