X-ray-determined structure of the technetium complex [Tc₂(-CO)₂(NC₅H₅)_{2(CO)6] revisited: [Tc2(-OMe)2(NC5H5)2(CO)6] as the correct formulation}

Some of us reported previously the structure of di-mu-carbonyl-bis[tricarbonyl(pyridine)technetium], [Tc-2(mu-CO)(2)(C5H5N)(2)(CO)(6)], as the main product of the reaction of [Tc-2(CO)(10)] with pyridine at room temperature, using the reagent itself as solvent [Zuhayra et al. (2008). Inorg. Chem. 47, 10177-10182]. On the basis of an X-ray analysis of the product, a molecular structure was proposed with two bridging carbonyls displaying very unusual geometrical features, not explained at the time. Subsequent chemical considerations, coupled with density functional theory (DFT) calculations, prompted us to revise the original structure determination. Using the original raw diffraction data, we have now performed new refinements to show that the previously proposed 'bridging carbonyls' actually correspond to bridging methoxide groups, and that the crystals analyzed at the time therefore would correspond to the complex di-mu-methoxido-bis[tricarbonyl(pyridine)technetium], syn-[Tc-2(mu-OMe)(2)(NC5H5)(2)(CO)(6)]. This methoxide-bridged complex likely was a minor side product formed along with the main product in the above reaction, perhaps due to the presence of trace amounts of methanol and air in the reaction mixture.