OXOVANADIUM(IV)-AMIDE BINDING - SYNTHETIC, STRUCTURAL, AND PHYSICAL STUDIES OF (N-[2-(4-OXOPENT-2-EN-2-YLAMINO)PHENYL]PYRIDINE-2-CARBOXAMIDO)OXOVANADIUM(IV) AND (N-[2-(4-PHENYL-4-OXOBUT-2-EN-2-YLAMINO)PHENYL]PYRIDINE-2-CARBOXAMIDO)OXOVANADIUM(IV)

The complexes [VO(pycac)] and [VO(pycbac)] were prepared by the reaction of bis(pentane-2,4-dionato)oxovanadium(IV) with either N-[2-(4-oxopent-2-en-2-ylamino)phenyl]pyridine-2-carboxamide (H-2pycac) or N-[2-(4-phenyloxobut-2-en-2-ylamino)-phenyl]pyridine-2-carboxamide (H-2pycbac) in a methanolic solution. Crystals of [VO(pycac)] crystallized from nitromethane were monoclinic, space group P2(1)/n with a = 7.5938 (1) angstrom, b = 30.161 (1) angstrom, c = 13.6982 (2) angstrom, beta = 86.468 (1)-degrees, Z = 8, and R(w) = 5.39%. Crystallization of [VO(pycac)] from chlorobenzene yielded triclinic crystals with a space group P1BAR and a = 7.8558 (5) angstrom, b = 12.934 (1) angstrom, c = 15.675 (1) angstrom, alpha = 78.594 (2)-degrees, beta = 89.938 (2)-degrees, gamma = 88.097 (2)-degrees, Z = 4, and R(w) = 6.45%. [VO(pycbac)] crystals were monoclinic, space group P2(1)/c with a = 6.5422 (4) angstrom, b = 14.4786 (8) angstrom, c = 19.963 (1) angstrom, beta = 93.461 (2)-degrees, Z = 4, and R(w) = 3.80%. The geometry about vanadium in each structure approximates a square pyramid with an average V=O bond length of 1.595 angstrom with the metal ion 0.669 angstrom above the basal plane. The average V-N (pyridine), V-N(amine), V-N(amide), and V-O bond lengths are 2.100, 2.045, 1.981, and 1.916 angstrom, respectively. The V-N(amide) and V-O bond lengths constitute rare examples of such short V-N and V-O distances that have been reported for oxovanadium(IV) complexes to date. In addition to the synthesis and crystallographic studies, we report the optical, infrared, magnetic, electron paramagnetic resonance, and electrochemical properties of these complexes. This study represents the first systematic study of oxovanadium containing a vanadium-amide bond.