AMIDATE LIGANDS FOR THE OXOVANADIUM(IV) CATION - DESIGN, SYNTHESIS, STRUCTURE, AND SPECTROSCOPIC AND ELECTROCHEMICAL PROPERTIES

With the goal of making vanadyl-specific ligands, the synthesis of a series of tetraanionic diamidate diphenolate ligands and their respective oxovanadium(IV) complexes is reported. The strongly sigma-donating ligands are constructed on a disubstituted propanediamide backbone, which stabilizes the highly oxidized vanadium(IV) center as evidenced by the remarkably low potential of -0.047 V (vs SCE) for the reversible VO3+/VO2+ redox couple of the oxovanadium(IV) dianion complex. This potential can be varied over a ca. 0.50 V range upon 5-substitution of the phenolato ring with electron-donating or -withdrawing substituents (e.g., methyl, chloro, or nitro). The strongly sigma-donating ligand environment provided by the diamidate-diphenolate ligands also results in relatively low nu(v = O) of 942-955 cm-1 for the series of complexes and values of 10Dq of ca. 21 000 cm-1. The structure of the potassium salt of [N,N'-bis(2-hydroxyphenyl)-2,2-diethylpropanediamido]oxovanadate(IV) is reported. The complex crystallizes in the space group P1BAR with unit cell parameters of a = 13.577 (4) angstrom, b = 14.006 (4) angstrom, c = 15.933 (5) angstrom, alpha = 115.03 (2)-degrees, beta = 114.16 (3)-degrees, gamma = 90.37 (2)-degrees, V = 2445 (4) angstrom3, and Z = 4. Final residuals for the refinement of 556 variables against 4320 data were R = 5.3% and R(w) = 7.0%. The structure contains two independent complex dianions which differ primarily in the conformation of the ethyl substituents of the propanediamide backbone and which exhibit the novel diamidate-diphenolate coordination to oxovanadium(IV).