Synthesis, characterization, and structure of molybdenum and tungsten trinuclear compounds with more than six cluster electrons
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1992
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Abstract
Synthetic methods for a series of new M3X13 type triangular trinuclear clusters with eight cluster electrons and a core of M3OX3 (M = Mo, W; X = Cl, Br) are described in this dissertation. The methods employed in the preparation of these complexes include the assembly reactions from MoCl3*3H2O, MoCl3(THF)3, MoBr3*H2O, and [Et4N]3[W2Cl9] in the presence of an excess amount of acetic acid and acetic anhydride. The redox behavior of these eight-electron species has also been investigated. Both cyclic voltammetry and synthetic results indicate that these eight electron species can be reduced to the ones with nine cluster electrons, but cannot be oxidized to the ones with seven or six cluster electrons without the cleavage of metal-metal bonds. Substitution reactions of terminal halides and bridging acetate ligands for these eight cluster electron complexes have also been studied. The studies show that these ligands are quite inert towards replacement reactions; however, during the reduction process these ligands become labile, and the substitution reactions of these ligands do occur. A total of twelve new molybdenum and tungsten trinuclear compounds with eight or nine cluster electrons have been structurally characterized by X-ray diffraction. Their structural features are presented in this dissertation. All of the experimental data are consistent with predictions of the theoretical calculations M3X13 type trinuclear compounds with the M3OX3 (M = Mo, W; X = Cl, Br) cores achieve the maximum stability when they have eight cluster electrons for metal-metal interaction, and continue to be stable when one more electron enters the antibonding 2e orbitals. Furthermore, the syntheses, characterizations, and structures of a butterfly tetranuclear compound and two edge-sharing bioctahedral complexes, which are the by-products of our attempted syntheses of the above trinuclear compounds, are also provided in this dissertation.
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Major chemistry