AN INVESTIGATION OF VANADIUM(2)-VANADIUM(3) COUPLE WITH POLYPYRIDINE LIGANDS

In harmony with earlier preliminary work, V(bipy)32+ has been shown to be a very much slower reducing agent than Cr- (bipy)32+. The vanadium(III)-polypyridine species formed as the immediate product of the oxidation of the V(II) complex has been shown to be very labile. Ligand is lost rapidly and disproportionation or further oxidation ensues so that a VO2+- polypyridine species is in fact the final product of the oxidation. Thus, although V(bipy)32+ does reduce Ru(NH3)63+, for example, E° for V(bipy)32+,3+ may in fact be much more negative than for Ru(NH3)62+,3+, the over-all reaction being driven by the instability of V(bipy)33+. Application of the “relative” Marcus theory to the rate data for a number of oxidants acting on vanadium(II)-polypyridine complexes suggests that E° for V(plpy)m2+,3+ is somewhat more positive than -0.8 V. Our study is inconclusive on the matter of whether the self-exchange in V(bipy)32+,3+ is significantly less rapid than for Fe- (bipy)32+,3+, for example. © 1968, American Chemical Society. All rights reserved.