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Mechanisms for water exchange from the bioxo-capped M-M-bonded trinuclear clusters, [[M3(mu3-O)2(mu-O2CCH3)6-(OH2)3].sup.2} [M = Mo)IV) and W(IV)] were investigated using high pressure [.sup.17.O]. Combination of these volumes with high-pressure [.sup.17.O] NMR data from other aqueous metal clusters establish strong link between the activation volumes and entropies, used to assign mechanisms for water-exchange reactions for different aqueous metal clusters.

A study of a ruthenium-based version of Barton's Gif(super IV)-type system (Ru(sub cat)/Zn/O2 in pyridine/acetic acid for the selective oxygenation of cycloalkanes using a range of analytical techniques is presented. The results show that formation of sec-alkylhydroperoxides in addition to monomeric divalent complexes such as trans-[M(o2CCH)(sub 2)(py)(sub 4)] (M =Fe or Ru) are key processes central to the mechanism of the Gif oxygenation process toward ring hydrocarbons.

X-ray crystal structural analyses and solution hydrogen nuclear magnetic resonance were used to analyze the syntheses of a variety of large macrocylic ligands and the corresponding dicopper(I) compounds. Findings showed that the structures of the dicopper(I) compounds of the ligands were similar to the solid-state structures. The structural similarity indicated that ligand preorganization is not a prerequisite for double-helical figure-of-eight structures.

Extended X-ray absorption final structure analysis was employed in the determination of the core arrangement of ruthenium in a symmetric adamantanoid. The tetrameric aqua ruthenium cation was analyzed in aqueous solutions of perchloric acid and nitric acid. The relevance of the the ruthenium ions to the core structure is described.

The exchange of water molecule with iridium(III) on the homoleptic mononuclear metal center (Ir(H2O)6)3+ involves an associative interchange mechanism. A negative volume and near-zero entropy of activation confirm the occurrence of this mechanism. This is the slowest water exchange of similar nature giving a rate constant of 1.1x10(super -10) s(super -1). The deprotonated (Ir(H2O)5(OH))2+ is more reactive than (Ir(H2O)6)3+. Water exchange on this species takes place through an interchange mechanism.

Aqueous solutions, trinuclear dioxo-capped acetato-bridged complexes and monooxo-capped complexes are subjected to experiments on energetic studies of complex growth and transfer of water. Reactions in the complex reveal an Id mechanism when energetic statistics of NCS-, C2O(sub 4)(super 2-) and CD3OD complexation are contrasted with that of transfer of water. Replacement of water by HC2O4(super-) in the complex occurs by means of a concerted process where C-O bond breakage is obtained from the outgoing water ligand.

The quantitative determination of the hydration structure of hexaaquairidium(III), [[Ir[([H.sub.2]O).sub.6]].sup.3+], the most inert aqua ion, in aqueous solution obtained by employing experimental-theoretical X-ray absorption spectroscopy and molecular dynamics simulations is presented.

A discussion on ligand substitution at inorganic centers is presented with emphasis given to reactions at cationic transition metal centers specifically involving water ligand exchange and replacement processes. Subtle changes to the coordination geometry, neighboring ligands, and marginal steric effects could profoundly affect the rate and mechanism of ligand substitution, a finding that is of direct relevance to the low symmetry inorganic centers present in biology.

Research has been conducted on dinuclear copper(I) complex. The authors have structurally characterized this complex, and report that they have observed intramoleculr ligand hydroxylation.