Physicochemical properties of technetium acido clusters

The review is concerned with the electronic and molecular structure and physicochemical properties of all types of technetium clusters with acido ligands described to date. As a typical cluster-forming metal, technetium possesses a number of specific, anomalous cluster-forming properties that can be interpreted in terms of greater capability of outer diffuse 5s(5p) AOs to participate in the formation of additional M–M bonds in technetium acido clusters as compared to analogous clusters of other transition d-elements. Theoretical interpretation of the electronic and molecular structure and properties of technetium clusters has been confirmed by experimental data (X-ray analysis, magnetochemistry, and EPR, optical, X-ray photoelectron and X-ray emission spectroscopy). The experimentally observed increased stability of technetium clusters with odd numbers of 'metallic' electrons and a decrease in the effective charge on Tc atoms upon formation of the M–M bonds are discussed. Recently found 'anomalous' properties of technetium and rhenium compounds with ferrocenium cations (in particular, unusual low-temperature electron emission on X-ray irradiation) are also considered. The bibliography includes 101 references.