Quantum Chemical Study of the Properties of Molecular Hydrogen Complexes of Osmium(II): A Comparison of Density Functional and Conventionalab InitioMethods

Abstract

The geometries of [Os(NH3)4Lz(η2-H2)](z+2)+ complexes, where molecular hydrogen is trans to the Lz ligand, have been calculated using density functional theory (DFT) and compared with the results of MP2 calculations. The quality of agreement between the DFT and MP2 geometries is found to be dependent on the trans ligand Lz. When Lz = acetone, water, acetate, and chloride, the agreement between the DFT and MP2 calculations is generally reasonable, and for the Lz = acetate complex, the DFT and the MP2 predictions are in acceptable agreement with the experimental geometry. When Lz = hydride, pyridine, acetonitrile, cyanide, hydroxylamine, and ammonia, the DFT calculations predict a much shorter H−H bond length and slightly longer Os−H distances when compared with the MP2 values. As the potential energy surfaces are very flat with respect to the H−H stretch, the differences between the DFT and MP2 geometries correspond to energy differences of approximately 3 kcal mol-1 when calculated at the same level of th...