Complex chemistry of technetium

Technetium, a true second row transition element, tends to form complex compounds. Oxidation states lower than +3 could be made with certainty only through complex stabilization. The existence of all known oxidation states of technetium from +7 to -1 has been verified in complex compounds. Coordination numbers from 4 to 9 and numerous coordination geometries have been seen. The magnetic moments of technetium complexes can be explained fairly well on the basis of crystal field considerations that show technetium to form low-spin compounds. 

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The knowledge of the chemical properties of technetium has grown over the years, as indicated hy review articles and books (Dewanjee 1990 Lever 1995 Nowotnik 1994 Peacock 1966 Schwochau 1983 Steigman and Eckelman 1992). Of particular interest are the Proceedings of the International Symposium on Technetium in Chemistry and Nuclear Medicine, presenting new developments in complex chemistry of technetium and rhenium, with state-of-the-art lectures, listed at the end of this chapter under Further Reading . 

Knowledge of the complex chemistry of technetium is primarily based on laboratory experiments using the isotopic tracers Tc (Ti/2 = 6.02h), Tc (Ti/2 = 2.6 X 10 years), Tc (T1/2 = 90 days), and Tc (Ti/2 = 61 days). In aqueous solution, the physicochemical forms of technetium will depend on pH and redox conditions (Eh). From Eh-pH diagrams it can be deduced that TcOT is the only stable physicochemical form in aerobic natural waters. Under anaerobic conditions, however, Tc04T is reduced to Tc02, TcO(OH)2, or TcCle". Technetium-species in oxidation state IV may associate with organic material such as humic substances in anoxic sediments, and thereby behave as organic colloids. 

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