ORIGIN OF THE UNUSUAL BENDING DISTORTION IN THE (MU-OXO)DIVANADIUM(III) COMPLEX [V2O(L-HIS)(4)] - A REINVESTIGATION

The title compound, [V2O(l-his)(4)].2H(2)O (1), originally reported by Kanamori et al. (Chem. Lett. 1993, 1731-1734), has been reinvestigated using both X-ray crystallography and resonance Raman spectroscopy. Redetermination of the structure in the higher symmetry monoclinic space group C2 gives the following crystallographic parameters: C24H34N12O11V2, fw = 786.5, a = 14.583(2) Angstrom, b = 14.024(2) Angstrom, c = 10.659(1) Angstrom, beta = 129.71(1)degrees, V = 1676.9(2) Angstrom(3), Z = 2, R = 0.0399 and R(w) = 0.0548 for 249 least-squares parameters refined against 3504 unique, observed (F > 4 sigma(F)) data. The X-ray structure reveals two strong intramolecular hydrogen bonds that account for the unusually small V-O-V angle (153.9 degrees) in this unsupporated mu-oxo divanadium complex. Resonance Raman spectroscopy in the solid-state confirms the presence of the intramolecular hydrogen bonding and the acute V-O-V angle. Comparison of resonance Raman spectra of 1 in solid and solution indicates that the V-O-V angle opens up to similar to 180 degrees upon dissolution due to a breaking of the intramolecular hydrogen bonds in the solid.