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-.