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We used a novel experimental setup to conduct the first synchrotron-based (61)Ni Mössbauer spectroscopy measurements in the energy domain on Ni coordination complexes and metalloproteins. A representative set of samples was chosen to demonstrate the potential of this approach. (61)NiCr2O4 was examined as a case with strong Zeeman splittings. Simulations of the spectra yielded an internal magnetic field of 44.6 T, consistent with previous work by the traditional (61)Ni Mössbauer approach with a radioactive source. A linear Ni amido complex, (61)Ni{N(SiMe3)Dipp}2, where Dipp = C6H3-2,6-(i)Pr2, was chosen as a sample with an "extreme" geometry and large quadrupole splitting. Finally, to demonstrate the feasibility of metalloprotein studies using synchrotron-based (61)Ni Mössbauer spectroscopy, we examined the spectra of (61)Ni-substituted rubredoxin in reduced and oxidized forms, along with [Et4N]2[(61)Ni(SPh)4] as a model compound. For each of the above samples, a reasonable spectrum could be obtained in ∼1 d. Given that there is still room for considerable improvement in experimental sensitivity, synchrotron-based (61)Ni Mössbauer spectroscopy appears to be a promising alternative to measurements with radioactive sources.

The synthesis, structural, spectroscopic and electrochemical properties of a series of high-spin thiolatonickel(II) through the reaction of [Ph[Tt.sup.tBu]]Ni(N[O.sub.3]) with thiols (RSH) in the presence of triethylamine are described. The presence of the electron withdrawing group on the thialato group has made the thiolatonickel(II) complexes very to easy to reduce.

Absorption, magnetic circular dichroism (MCD), and variable-temperature variable-field MCD (VTVH-MCD) spectroscopic techniques are employed in conjunction with density functional theory (DFT) electronic structure calculations to generate an validated description of Ni-C bonding in [Ni(tmc)CH3](super +). Spectroscopic and density functional theory (DFT) computational studies afford a quantitative bonding description for [Ni(tmc)CH3](super +) that reveals a highly covalent Ni-CH3 bond.

Resonance Raman (rR) spectroscopic and density functional theory (DFT) computational studies on a trans-mu- 1,2-peroxo-bridged [Ni(super 2+)(sub 2)] complex, [{(tmc)Ni(super 2+)}(sub 2)(O(sub 2)](super 2+) where tmc = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane, are presented and discussed. These studies provide a quantitative comparison between Ni-peroxo and Cu-peroxo bonding.

The dominant O -> Ni CT transition of [(PhTt(super tBu))2Ni2(mu-O)2] observed at 17700 cm(super -1) is red-shifted by ~7000 cm(super -1) relative to the corresponding transition in bis-mu-oxo(Ni(super 3+))2 dimers with nitrogen supporting ligands. This red-shift along with a relatively low Ni-O bond strength are primarily due to the presence of the thioether ligands in [(PhTt(super tBu))2Ni2(mu-O)2] that directly influence the characters of the Ni2O2 core MOs.

Research has been conducted on the borato ligands' nickel complexes. The preparation, characterization and electrochemical properties of these complexes have been carried out and the details are reported.

Results indicate the solution and solid state structures of copper(I) thioether complexes are influenced by the borato ligand they contain. Complexes containing smaller (methylthio)methyl donors yield tetrameric species, while those containing larger (arylthio)methyl groups form monomeric and one-dimensional extended structures in solution and solid state, respectively.

The syntheses and molecular structures of a series of tetrahedral zinc complexes designed to model the active sites in Escherichia coli methionine synthases are described. The tridentate ligands provide the appropriate donor atoms, [S3] and [S2N], to accurately model the catalytic zinc sites in the methionine synthases from E. coli.

A new sulfur-rich tridentate ligand, tetrakis(2-thienyl)borate (1-) was synthesized. Its reactivity and other characteristics were by molecular orbital analysis of its coordination to a metal center. Unlike the analogous tetrakis((methylthio)methyl)borate (2-), 1- does not coordinate Mo(CO)3 when reacted with (C7H8)Mo(CO)3. The sulfur atoms in both ligands are oriented to coordinate the metal in a pyramidal eta1 sulfur-bound mode. Approximate molecular orbital computations were employed to compare the metal-ligand interactions in these related species. Findings indicated that the magnitude and polarizability of the electronic charge density of the lone pairs on the sulfur atoms determine the coordination strength of the ligands.

The synthesis and characterization of the Fe(II), Co(II) and Ni(II) derivatives of the tridentate, face-capping tetrakis( methylthio methyl)borate and phenyltris( methylthio methyl)borate are described. Structural analysis showed that two ligands coordinate with the metal ion in an S6-coordination environment of Oh symmetry. The Fe(II) complexes were found to show spin-crossover behavior while the Co(II) derivatives are low spin.

The formation of the high spin, five coordinate derivatives involves the reaction between RRSS (Ni{tmc}SC6H5)(OTf) and RSRS(Ni{tmc}SC6H5)-PF6 isomers of( Ni{tmc})(OTF)2 and NaSC6H5. The molecular structures of these derivatives are determined by X-ray diffraction. The isomers vary in their structures. Nickel thiolates react with haloalkanes giving a second order rate constant and RRSS isomer reacts 350 times faster than the RSRS isomer. RRSS isomers crystallizes in monoclinic space group. A square planer coordination enviornment is provided to the Ni(I) ion with two distinct Ni-N bond distances.

A trans-[mu]-1,2-disulfido complex of nickel is spectroscopically identified and characterized. The studies have supported this core structure and have disclosed rather long Ni-S and S-S bonds.

The initial effort to prepare binuclear complexes containing a methylnickel moiety is reported. The results provide insight into their dynamic properties and reactivity to further understand organonickel catalysis in biology.

Two new and complementary synthetic routes, namely, the activation of elemental sulfur by nickel(I) and the thermal decomposition of Ph[Tt.sup.tBu]]Ni[(SC[Ph.sub.3]).sup.20]).sup.20] via C-S bond cleavage, to a disulfidodinickel(II) complex are described. The result from studies establishes the reaction of nickel(I) with elemental sulfur as a new synthetic strategy for the preparation of sulfidonickel adducts.

A series of low-coordinate, paramagnetic iron complexes in a tris(thioether) ligand environment are prepared. It is shown that 2 equiv of adamantly azide has undergone a 3 + 2 cycloaddition at monovalent iron phosphine complexes, yielding high-spin dialkyltetraazadiene complex.

The electron-transfer mechanism involved in methyl transfer from methylcobaloxime to (triphos)Ni([PPh.sub.3]) is being described. The mechanism involved is found to be the same that is used in acetyl coenzyme A synthase/carbon monoxide dehydrogenase (ACS/CodH).

An analysis of two unique molecular systems, which have given way to a novel nickel-dioxygen structure, types, monomeric side-on and end-on superoxo and trans-mu-1, 2-peroxo-dinickel complexes is done. Advanced spectroscopic techniques including resonance Raman and x-ray absorption spectroscopies, along with density functional theory analyses are applied to determine the geometric and electronic structures of the complexes.

The preparation, spectroscopic characterization and reactivity of a [Ni.sup.2+]-superoxo complex are reported. The [Ni(tmc)([O.sub.2])](OTf) (3) represents the first example of an end-on dioxygen complex in nickel coordination chemistry, while the diverse Ni/[O.sub.2] adducts have provided the opportunity to evaluate inherent reactivity differences between the two coordination modes.

The nickel (I) complex [PhTt(super Ad]Ni(CO) (PhTt(super Ad)), phenyltris((1-adamantylthio)methyl)borate) reacts with O(sub 2) generating a 1:1 species identified as a side-on dioxygen adduct based on its spectroscopic properties as supported by DFT computational results and by its reactivity. The successful pursuit of the strategy, which led to the discovery of a side-on dioxygen complex of nickel, is reported.

The fundamental properties of the Cys-Gly-Cys motif, by exploring the Ni binding preference of the short peptide in the absence of the protein superstructure, are discussed. The resulting square planar Ni(CGC) metallopeptide from this binding is a building block for the construction of larger structures related to A synthase/CO dehydrogenase active site.

Research has been conducted on Ni (super)+ four-coordinate complex. Results demonstrate that this complex serves as a Ni-CO reaction intermediate in the acetyl-CoA synthase catalytic cycle.

The first preparation of thiolate-bridged nickel-copper binuclear complexes is reported. The acetyl coenzyme catalyzed reaction entails the reversible assembly of acetyl CoA through the coupling of a methyl substituent from enzyme-bound methylcobamide, CO and the thiolate, CoA.

The characterization of a NiIII2(mu-O)2 core has been undertaken with regard to dioxygen activation by a nickel thioether compound.

Research into the preparation of cobalt(III) and nickel(II) complexes in which thioether donors support the organometalloid fragment is presented.