Critical Factors in the Synthesis of tris Complexes of Chromium(iii) with 2,2′-Bipyridine and 1,10-Phenanthroline

The preparation of tris(2,2′-bipyridine)chromium(III) by oxidizing the corresponding chromium(II) complex should be carried out in such a manner that the initial oxidation product (the tris complex) is protected from reaction with constituents of the remaining unoxidized solution. There is evidence to believe that the 1,10-phenanthroline analog should be treated similarly. The tris-chromium(II) complex is in equilibrium with diaquobis-chromium(II) complex which can undergo an electron exchange reaction with tris-chromium(III). The various important reactions are characterized and suggestions are made for improving the yield and purity of the preparation.