by X-ray diffraction. Complexation of these ligands with vanadium in aqueous solution has been studied by pH potentiometry, UV/Vis, and circular dichroism (for the L-Tyr derivatives), as well as by EPR for the VIVO systems and 51V NMR for the VVO2 systems. Stoichiometries and complex formation constants have been determined by pH potentiometry (25 °C, I = 0.2 M KCl) 1:1 complexes are formed in most systems