The effect of amide coordination on the parallel coupling constant has been determined for three square pyramidal vanadyl complexes. The complexes (VO)-O-IV(PAAP), (VO)-O-IV(PAIS), and [(VO)-O-V(HIBA)][C4H9)(4)N] have been prepared, and the tatter two have been structurally characterized (PAAP is the dianion of 1,2-bis(2-carboxamidopyridyl)-benzene, PAIS is the dianion of [N-(salicylideneamine)phenyl]pyridine-2-carboxamide], HIBA is the tetraanion of 1,2-bis(2-hydroxy-2-methylpropanamido)benzene). X-ray diffraction quality crystals of (VO)-O-IV(PAIS> were obtained by slow evaporation of a nitromethane solution of (VO)-O-IV(PAIS). X-ray parameters for (VO)-O-IV(PAIS) : C19H13N3O3V1, 382.08 g/mol, P2(1)/n, a = 7.777(3) Angstrom, b = 18.433(7) Angstrom, c = 11,565(4) Angstrom, beta = 102.66(3)degrees; V = 1633(1) Angstrom 3; Z = 4. The final. refinement yielded R = 0.0600 and R(w) = 0.0450. X-ray diffraction quality crystals of [(VO)-O-V(HIBA)][(C4H9)(4)N] were obtained by slow evaporation of a THF-CHCl3 solution of [(VO)-O-V(HIBA)-[[(C4H9)4N]. X-ray parameters for [(VO)-O-V(HIBA)][C4H9)(4)N] : C(30)H(52)N(3)0(5)V(1), 585.69 g/mol, P2(1)/n; a 13.228(3) Angstrom, b = 16.054(4) Angstrom, c = 14.7140(20) Angstrom, beta = 93.240(10)degrees; V = 3119.7(11) Angstrom(3); Z = 4. The final refinement yielded R = 0.051 and R(w) = 0.047. Comparison of calculated and experimental values of A(II) for vanadyl-bleomycin and vanadyl-serum albumin support the presence of a deprotonated amide donor(s) in vanadyl-bleomycin but not in vanadyl-serum albumin.