Investigation of the structure and bonding of metal complexes through the use of density functional theory
Density functional theory has been used to investigate the structure, bonding and spectroscopic properties of a variety of interesting and potentially useful inorganic complexes. The photoluminescent (CuN(SiX3) 2)4 complex has an unusual square geometry with no formal Cu-Cu bonding. TDDFT calculations were performed to investigate the origin of the photoluminescence. It was determined that the complex undergoes a significant change in geometry in the cluster-centered, weakly Cu-Cu bonding, excited state. Another unusual copper cluster, Cu3(OL2C X)6, was also examined. This complex is triangular, paramagnetic, and has no formal Cu-Cu bonding. The complex is spin-frustrated, resulting from the arrangement and interaction of the three unpaired electrons on the Cu centers. The EPR parameters were calculated and the possibility of Jahn-Teller stabilization of the doublet state was investigated.
The majority of this work focuses on the structure, energetics and bonding of series of isomeric transition metal complexes. There are a surprising number of “missing” (as of yet unobserved) simple, linear, sandwich complexes that could be formulated with transition metals and CnHn rings from n = 3 to n = 8. The Group 6 MC12H12 isomers [(η6-C6H6)2M, (η 5-C5H5)M(η7-C7H 7), (η4-C4H4)M(η 8-C8H8)], Group 8 MC10H10 isomers [(η5-C5H5)2M, (η5-C4H4)M(η6-C 6H6), (η3-C3H3)M(η 7-C7H7)] and NiC8H8 isomers [(η4-C4H4)2Ni, (η 3-C3H3)Ni(η5-C5H 5)] were studied, The NiC8H8 study was extended to include (η2-C2H2)Ni(η 6-C6H6) and (η8-C8H 8)Ni. The ground-state geometry was determined for all isomers, and bonding analysis was performed to determine the dominantly bound fragment in all the species, It was found that, in general, the distance between the metal and ring centroids was long for π-bound rings and significantly shorter in δ-bound rings. The out-of-plane bending of the C-H bonds in the ring ligands varied according to how mismatched the ring π orbitals were in relation to the M δ orbitals. The bonding analysis found that the dominantly bound rings were not necessarily those with π bonds, the most covalent character, or best size match, Each complex was analyzed individually to determine the dominantly bound ring, and to understand the interactions. Attention was paid to the changes seen as the metal was changed both moving across and down the transition metal block.