Experimental and computational studies of the metal-metal stretching vibration in X(3)MMX(3) compounds (X = alkoxide, alkyl, amide).
Raman spectra of a number of triply bonded M(2)X(6) (M = Mo, W; X = alkoxide, alkyl) compounds have been obtained. Several exhibit a band assignable to the metal-metal stretching vibration nu(M)(M). This band was not identified in earlier studies of the M(2)(NMe(2))(6) compounds. We have attempted to correlate the Raman vibrational data with structural data from single-crystal X-ray diffraction studies. Diffraction studies of the M(2)(O-1-4-pentyl[2.2.2]bicyclooctyl)(6) species show a crowded environment around the dimetal core, but the M-M-O angles differ substantially from 90 degrees. Thus, this angle does not solely determine the extent to which the metal-metal and ligand-based vibrational modes couple and, in turn, our ability to observe nu(M)(M). Computational studies of model systems confirm the assignment of the band as being nu(M)(M), although the predicted vibrational energies are consistently too high by ca. 7%. The computational results suggest that a nu(M)(M) band may be present in the published spectra of the M(2)(NMe(2))(6) pair.
Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, Illinois 60115, USA. tgilbert@marilyn.chem.niu.edu
Thomas M
TM
Gilbert
John C
JC
Littrell
Chad E
CE
Talley
Michael A
MA
Vance
Richard F
RF
Dallinger
Robin D
RD
Rogers