The application of density functional theory to inorganic and organometallic systems.

摘要

The research presented here involves the application of density functional theory to inorganic and organometallic systems. The first chapter serves as an introduction to density functional theory. In the second chapter, we applied various non-local density functionals to four problems in inorganic chemistry that have proven difficult in the computation of accurate conformational or reaction energetics. We then compared these DFT results with those from post-Hartree-Fock ab initio methods and with experiment, when possible. We found that all four of the functionals under investigation performed quite well compared to MP2 calculated geometries, with B-P86 achieving the overall smallest average absolute deviations in bond distances relative to MP2. We also found that the choice of the exchange functional is much more important than the choice of correlation functional for most of the systems we examined.; Because DFT performed so well when compared to ab initio methods, we used DFT to examine the conformational preference of C₂X₄ -bridged bimetallic transition metal complexes in the third chapter. Specifically, we used DFT to examine the relative energetics of dithiolene-like vs. dithiocarbamate-like isomers of (Cp₂Ti)₂(μ-C ₂X₄) where X = S and Se, and [(PH₃)₂M] ₂(μ-C₂X₄) where M = Cu and Ag and X = O, S, Se and Te. We found that the dithiolene-like isomer is the preferred conformation for all of the systems investigated. An examination of the metal-chalcogen overlap populations for each conformation and the metal-chalcogen overlap populations for the Hartree-Fock molecular orbitals involved in metal-bridge bonding for each species revealed that this preference is due to better overlap between the metal and the bridge in the dithiolene-like conformation.; Finally, in an appendix we reported ab initio and density functional calculations for two potentially stable carbenes, pyrazole-3-ylidene and pyrazole-4-ylidene. We found through calculations of singlet-triplet gap energies, proton affinities and relative metal-ion affinities that pyrazole-3-ylidene is more stable than pyrazole-4-ylidene, but that neither is as stable as the previously investigated pyrazole-2-ylidene.