A force field for vanadium-oxos was developed and tested with a variety of complexes with coordination numbers of 5 or 6 and formal oxidations states of +4 or +5 on the metal. Similarly, a semiempirical quantum mechanical method for transition metals was extended to vanadium. In this research soft and hard ligands were studied, as were ligands coordinated through single, multiple, and dative bonds. Despite the diversity of vanadium coordination chemistry, generally good modeling is achieved in a fraction of the time with less computational resources using molecular mechanics and semiempirical quantum mechanics. The L 4 V 4+ O and L 5 V 5+ O groups were emphasized given their prevalence and importance. In general, the predictive ability was superior for the former structural motif. The combination of molecular mechanics and semiempirical quantum calculations provide an effective and efficient tool for analysis of the steric and electronic energy differences between isomers.

A computational study of vanadium peroxides (L n V(O 2 ) m ; m ) 0-4), important for their biochemical and catalytic activity, is reported. In the compounds studied, ancillary ligands (L n ) are generally the hard, oxygen-and nitrogenbased donor ligands, e.g., carboxylates and pyridines, prevalent in the coordination chemistry of vanadium peroxides. The utility of estimating missing metal-dependent molecular mechanics (MM) parameters from quantum calculations is demonstrated. Given the limited vibrational data for many families of transition metal complexes, quantum calculations are a viable source for parameters to use in development of force fields. A conformational search of [V(O 2 ) 3 F] 2using MM yielded a geometry inconsistent with experiment, but consistent with ab initio geometry optimizations. A reinvestigation of this structure is therefore of interest. Molecular mechanics provides a quick and accurate method for obtaining structural information. The level of agreement for structural prediction is competitive with that obtained using more computationally intensive methods in much less time. In most cases it was seen that MM and quantum predictions reinforced each other, lending greater confidence in modeling results. In other cases, classical and quantum results were in conflict, indicating the need for further higherlevel, quantum calculations. Hence, MM and low-level quantum calculations, when used together, provide a valuable method for quickly probing the conformational space of large coordination complexes.

Page 3797. In paragraph 4, sentences 1 and 2, the erroneous ν(NO) values have been referred to; the sentences should read as follows: As expected, the ν(NO) bands in the IR spectrum of 3 were shifted to lower energy in comparison to those of 2; ν(NO) ) 1917 and 1903 cm -1 for 2, 1902 and 1890 cm -1 for 3, in KBr. The carboxylic acid substituents discussed above have the opposite effect on the nitrosyl stretching bands in comparison with the electron-donating methyl substituents in the bpy rings in this case. ) 0.05 Å) and ab initio (RMS ic ) RMS heavy ) 0.03 Å) techniques discussed in our paper are in excellent agreement with the experimental structures subsequently provided to us by Professor Thompson. We thank Professor Thompson for bringing his work to our attention.