Transition metal compounds with metal-metal multiple bonds play an important role in inorganic, materials, bioinorganic and organometallic chemistry. One element whose metal-metal bond chemistry is not well developed is technetium, the lighter rhenium congener. As of the year 2005, the number of complexes with multiple Tc-Tc bonds was quite limited: 25 dinuclear species, 4 hexanuclear and 6 octanuclear halide clusters had been structurally characterized; For the last decade, we have focused on expanding the chemistry of dinuclear complexes.Dinuclear technetium complexes consist of Tc2n+ unit (n = 4, 5, 6) coordinated to ligand. In these system, the Tc2n+ unit can exhibit bond orders between three and four. A fundamental question in the coordination chemistry of metal-metal bonded complexes is how changes in charge and electronic configuration of the metal in the M2n+ unit affect the metal-metal separation. For dinuclear technetium complexes, it might be anticipated that a decrease of bond order moving from a Tc26+ core to Tc24+ would be accompanied by an increase in the metal-metal separation; in fact, the opposite is observed, viz., a contraction of the Tc-Tc separation occurs with decreasing bond order. This phenomenon has been qualitatively explained by suggesting that contraction of 4d orbitals with increasing charge on the metal leads to less favorable overlap and somewhat weaker bonds. until recently no quantitative theoretical analyses have been performed.During the last decade, we focused on understanding the relationship between bond order and metal-metal separation in dinuclear complexes. Nine dinculear complexes (i.e., (n-Bu4N)2Tc2X8, Tc2(O2CCH3)4Cl2, Tc2(O2CCH3)2Cl4,  Tc2X4(PMe3)4 and cesium salts Tc2X83- (X = Cl, Br)  have been prepared and their electronic structure investigated by experimental and theoretical methods. Here, we review the preparation, molecular and electronic structure as well as the spectroscopic properties of those dinuclear complexes.

A decade of technetium dinuclear complexes with multiple metal-metal bonds

248th National Meeting (2014)

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