Rhenium divalent, complexes

Many compounds of technetium and rhenium are of analogous composition and of corresponding physical and chemical properties. Because of the very similar ionic radii, isotypic crystal structure formation of analogous compounds could often be observed. Technetium remarkably differs from manganese by the high stability of pertechnetate compared with permanganate. Moreover, divalent technetium does not exist as a hydrated ion but only as a stabilized complex. 

It is noted [181] that mononuclear complexes of divalent rhenium are rare, and coordination of two different radical ligands to a single metal is also unique. ... 

Reaction takes place under photolytic conditions at 0°C under N2. The product is a complex of divalent rhenium with three carbonyl ligands, one anionic monodentate 3,5-di-/-butyl-2-iminophenolate ligand, and one anionic chelating 1-hydroxy-2,4,6,8-tetra-r-butylphenoxazinyl ligand... 

These early successes with carbonyl complexes of rhenium encouraged me to undertake systematic research on the carbon monoxide chemistry of the heavy transition metals at our Munich Institute during the period 1939-45, oriented towards purely scientific objectives. The ideas of W. Manchot, whereby in general only dicarbonyl halides of divalent platinum metals should exist, were soon proved inadequate. In addition to the compounds [Ru(CO)2X2] (70), we were able to prepare, especially from osmium, numerous di- and monohalide complexes with two to four molecules of CO per metal atom (29). From rhodium and iridium (28) we obtained the very stable rhodium(I) complexes [Rh(CO)2X]2, as well as the series Ir(CO)2X2, Ir(CO)3X, [Ir(CO)3]j (see Section VII,A). With this work the characterization of carbonyl halides of most of the transition metals, including those of the copper group, was completed. 

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