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Spatial extensions of excited states of metal complexes are discussed relative to tunability by chemical variation. The metal d and/or MLCT character of triplet states is related positively to the size of zero-field splitting (zfs). Increasing metal character changes many properties. Ligand-ligand coupling changes as does the tendency to delocalize excitation, both being more exaggerated. For the first time properties of partially and completely deuterated Pt(2-thpy)(sub.2) compounds have been studied and results have been compared with those for a perprotonated compound.

Bis(phenoxyl)metal complexes of copper(II) and zinc(II) are discussed relative to their intramolecular spin interactions. Two complexes which contain two coordinated phenoxyl ligands in cis position relative to each other are described. Electronic structures have been studied with EPR spectroscopy. Spin interactions are different from those reported for analogous bis(semiquinonato)metal complexes.

A two-step, high-yield synthesis of (RhCl2-(Ph)(PPh3)2) starting from RhCl3*3H2O and SbPh3 through (RhCl2(Ph)(SbPh3)3), a density functional analysis with geometry optimization of the model molecule (RhCl2(PH)(PH2CHCH2)2) and an X-ray analysis of the monoclinic crystals is described. Results demonstrate a new efficient, synthetic route to stable organometallic compounds which can serve as starting materials for various preparative strategies.

Research was conducted to examine the remarkable influence of axial pi* coordination on the Cr-Cr quadruple bond in dichromium paddlewheel complexes. The study focused on new, definitive examples that demonstrate how donation of electrons to the pi* orbitals can weaken and lengthen the Cr-Cr bond. Results indicate that the cumulative effect of donation from four nitrogen atoms is very large, which is 0.4 angstrom in the Cr-Cr distance.

The various binding modes of lead in its divalent and tetravalent oxidation states are described. An analysis of high-resolution, high-precision crystal structures and ab initio molecular orbital optimizations of several gas-phase lead complexes were conducted. Objectives of the study include the identification of the conditions influencing the stereochemical activity of the lone pair of of Pb(II) electrons and to analyze conditions related to coordination numbers and preferred ligands. Results indicate that the lone pair orbital has little or no p character when the geometry is holodirected.

The electronic structure of the cluster compound alpha-Nb3Cl8 and the intercalated phase beta'-NaNb3Cl8 were examined. The crystal structures of the two compounds were found to consist of layers of interconnected Nb3Cl13 units. Photoelectron spectroscopy and band structure calculations showed well separated sets of Cl 3p levels at lower energy and Nb 4d levels of higher energy.

The synthesis and characterization of a trinuclear molybdenum cluster with 7-d electrons, (Cp*Mo)3S4, are presented. The complex has been prepared by the reduction of Cp*Mo(StBu3) by Na/Hg. The results of extended Huckel molecular orbital calculations on (CpMo)3S4 showed that the unpaired electron resides in the 2e orbital, which is antibonding with respect to the cluster atoms. A subtle distortion of the cluster has been attributed to the Jahn-Teller effect.

The electronic structure of (Ta5 NH super4 Cl17)6- cluster has been determined by molecular orbital calculations. The results showed a flat pyramidal cluster that exhibits an ordering of metal-metal bonding orbitals and capping in the basal-bridging imido ligands. The metal-metal bonding is limited to apical-basal bonding with no significant bonding between the basal metal atoms.

The stereochemistry of seven-coordinate main group and transition metal molecules were investigated by ab initio quantum chemical calculations. The results showed that the main groups are predominantly pentagonal bipyramidal. Transition metal molecules are either capped octahedral or capped trigonal prismatic. Analysis also showed that the ligands distort the charge density of the central atoms.

A study was done on the nearly octahedral hexamethylsulfur and hexamethylselenium molecules using the self-consistent-field molecular orbital theory. Results show that only D3 symmetry is predicted with a double-sigma basis set augmented by d-polarization functions on the central atom. The minima were also noted to be only slightly distorted from octahedral ligand coordination. In addition, molecular geometries, vibrational frequencies and infrared intensities were also predicted.

Research determined the molecular arrangements of two copper(II) dipeptide complexes with the use of the combined electron paramagnetic resonance spectroscopy, second derivative displays and computer simulation techniques. The ionic and covalent nature of the metal-ligand bonds of the two copper dipeptides, Cu-GlyHis and CuHisGly complexes, are also examined. Results show two different dipeptide arrangements in the first coordination sphere. The combined approaches was also found to be effective in identifying a set of spin Hamiltonian input parameters for the copper dipeptides.

The pentagonal-bipyramidal (PBP) complex diaqua(2, 6-diacetylpyridine bis semicarbazone) (DAPSC)iron(2) can serve as an intermediate neglect of differential overlap model for the optimum geometry examination of PBP structures. The geometry optimization calculations have shown the presence of singlet, triplet and quintet spin states. The quintet spin state, which features the lowest overall energy, exhibits bond distances and associated angles that are consistent with previously derived results. In addition, the reproducibility of the DAPSC ligand's planarity indicates that the PBP structure is in its empirical form.

Molecular orbital calculations were performed on (HN)U(NH2)3 and (H3SiN)U(N SiMe3 2)3 using discrete variational local density functional method. Results showed that the ionization energy of the imido group's N 2p(pi) level was greater than that of the amido group. Moreover, relativistic and nonrelativistic calculations were done to determine the effects of uranium-nitrogen bonds and ionization potentials to molecular orbital ordering. In addition, a simultaneous photoelectron spectrometric analysis was used to compare the derived transition-state energies.

A number of homoleptic pz complexes of titanium(IV) were synthesized and characterized. These species are the first homoleptic monomeric pz complexes of any metal and have only eta2-pz ligands. Results obtained from molecular orbital computations explain why the eta2-bonding mode is preferred and suggest that eta2-pz complexes should be common in early to middle transition metals.

A spectroscopic study of the quadruple coupling and pi* populations of the complexes W(PO3Me3)(CO)5, W(PMe3)(CO)5 and W(NMe3)(CO)5 allows a comparison of the pi-acceptor properties of trimethylphosphine with those of the phosphite and amine ligands. The study shows that antibonding pi-orbital populations (2-pi)x are enhanced more by ligand replacement of radial than of axial carbonyls. More important, the change in axial (2-pi)x in W(PMe3)(CO)5 is closer in value to that of W(PO3Me3)(CO)5 than that of W(NMe3)(CO)5, thus confirming that trimethylphosphine is a stronger pi-electron acceptor than the pi-neutral amine ligand.

The quantitatively large difference in the valence-electron distributions of the transition states of 17- and 18-electron transition-metal complexes is reflective of their substitution reaction rates. The substitution reaction of a 17-electron complex has a more stable transition state than an 18-electron complex. This is due to the deviation of the 19-electron transition state's two maxima away from the entering/leaving ligands. Contrastingly, the 20-electron system, which is the transition state of the 18-electron complex, features valence-electron charge concentrations that are placed adjacent to the entering/leaving ligands.

Ab initio electronic structure techniques are utilized in the investigation of the low-valent actinide complexes U(CH3)3, Np(CH3)3 and Pu(CH3)3. Complete active space calculations are performed in a valence double zeta basis set involving relativistic effective core potentials. The optimum geometry for both the pyramidal and planar AnMe3 forms are determined for the ground electronic state of each molecule. Results show a preference for the pyramidal structure, arising from the involvement of the 6d character in the An-C bonding orbitals as a function of bending angle.

Molecular or crystal orbitals of condensed octahedral niobium cluster networks can be constructed qualitatively from the Nb-Nb bonding molecular orbitals of the monomeric Nb6O18 cluster. The Nb-Nb and Nb-O interactions are analyzed to examine the optimal cluster electron counts in the bonding of these networks. Results agree well with the magic cluster counts observed in oxoniobates through experiments and previously devised counting scheme.

The computation of zero-field splitting tensors in transition metal complexes for any value of the ground-state total spin was discussed. The calculation was performed using an effective Hamiltonian technique to second order for orbitally nondegenerate ground states. Experimental results showed that the use of free-ion values for spin-orbit coupling and related constants in the examination of experimental data results in values for molecular orbital coefficients that overestimate the metal-ligand covalency.