Rhodium complexes oxalate

An analogous two-electron reduction of a rhodium complex has also been achieved by photolyzing the rhodium(III) oxalate complex mer-[RhX(C204)(py)3] (X = Cl, Br) to give the rhodium(I) complex RhX(py>3 (Ref. 137) ... 

To illustrate, Cotton and co-workers were able to synthesize a triangle based on a di-rhodium -90° acceptor subunit and oxalate bridging units 21). The di-rhodium complexes served as the vertices of the triangle, while the oxalates served as ditopic, chelating sides (Figure 1). 

Obtained by these methods rhodium trichloride is a red powder, insoluble in water and in acids. It is decomposed by concentrated aqueous potash, the resulting solution behaving like that of rhodium sesquioxides in the alkalies. It dissolves in concentrated solutions of potassium cyanide and of alkali oxalates, yielding complex cyanides and oxalates respectively. 

The synthesis of the ds-tetraamminedichlororhodium(III) ion, using the reaction of tetraammine[oxalato]rhodium(III) perchlorate with boiling 6 M hydrochloric acid, was first reported in 1975. The oxalato complex is formed by the reaction of pentaamminechlororhodium(III) chloride with oxalate and oxalic acid in water at 120°. The synthesis has been repeated on numerous occasions in our laboratory, and we have found that only in a minority of cases is it possible to isolate [Rh(NH3)4(C204)]C104 H20 in sufficiently pure form to prepare the pure perchlorate by recrystallization. In a majority of cases the product that precipitates from the reaction mixture on addition of perchloric acid contains an appreciable quantity of an unidentified impurity that is not removed by recrystallization. The procedure given below permits the preparation of pure cis-[Rh(NH3)4Cl2]CH/2H20 from the latter crude, impure oxalato complex. 

Werner resolved the tris oxalate using strychninium ion in 1912. Other effective resolving agents for the tris complex include (+ )-tris(l,10-phenanthroline)nickel(II), ( + )- or (- )-tris(ethylenediamine)cobalt(III) and (- )-tris(ethylenediamine)rhodium(III). The (- )-[Co(ox)3] ion has been studied by single-crystal methods and has the d configuration. It has been related to (-i-)-[Cr(ox)3] by X-ray powder photography, so its absolute configuration is also established as d by the more exact form of the rule of least-soluble diastereoisomers. ... 

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