EPR Evidence for Chromium(V) Binding to Phosphate and Pyrophosphate: Implications for Chromium(V)−DNA Interactions

Reactions of Cr(V) with phosphate and pyrophosphate were examined as models for ligand exchange binding to DNA and deoxyribonucleotides. The initial Cr(V) complex, [Cr(ehba)2O]-, can undergo ligand exchange with either one pyrophosphate, to form [Cr(ehba)(H2P2O7)O]-, or two pyrophosphates, to form [Cr(H2P2O7)2O]-, with a concomitant geometry change from trigonal bipyramidal to square pyramidal. Reaction with free phosphate produces two less stable monodentate Cr(V)−phosphate complexes which are assigned as meridional and facial isomers of cis-[Cr(ehba)2(H2PO4)O]2-.