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.

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A variety of approximate methods for efficient modeling of large lanthanide (Ln) complexes were studied. Attention was paid to ligand motifs prevalent in Ln coordination chemistry. Gadolinium was chosen given its central location in the Ln series and its importance in areas such as magnetic resonance imaging. A semiempirical approach based on a technique first described for europium was extended to gadolinium. Comparison with ab initio, molecular mechanics, and PM3 methods was performed for experimental and model complexes. Electrostatic models were found to be most reliable for cationic, large coordination number complexes with hard nitrogen and oxygen donorsan important subset of lanthanide complexes. When used for appropriate target complexes electrostatic models, particularly when used in conjunction with molecular mechanics, can be an effective and efficient technique for the study of large, experimentally relevant lanthanide coordination complexes.