SYNTHESIS, STRUCTURE, AND SPECTROSCOPIC PROPERTIES OF VANADIUM(III) AND VANADIUM(IV) COMPLEXES CONTAINING HYDRIDOTRIS(PYRAZOLYL)BORATE LIGANDS .3.

A series of vanadium(III) and -(IV) complexes of the type [L2V]BPh4, [LVCl2DMF], [LVOClDMF], and [LVO(acac)] where L is either the anion of hydridotris(pyrazolyl)borate, HB(pz)3, or hydridotris(3,5-dimethylpyrazolyl)borate, HB(Me2pz)3, have been synthesized and characterized by elemental analysis, molar conductance, electrochemistry, magnetic, UV-vis, IR, and ESR techniques. In all cases, the metal ion is in a distorted octahedral environment, facially coordinated to a tridentate hydridotris(pyrazolyl)borate ligand of varying steric bulk. The structures of the complexes of the type [L2V]BPh4 have been determined by single-crystal X-ray diffraction. Crystal data for [[HB(pz)3]2V]BPh4 are as follows: space group P1BAR with a = 12.796 (1) angstrom, b = 15.305 (2) angstrom, c = 11.285 (1) angstrom, alpha = 94.38 (1)-degrees, beta = 104.248 (9)-degrees, gamma = 108.64 (1)-degrees, V = 2000.7 (5) angstrom 3, and Z = 2. In general, comparison of the structural and physicochemical properties among the series reveals the expected effects of the electron-releasing methyl groups but few if any differences between analogous complexes that can be attributed to steric bulk. However, electrochemistry does demonstrate significant differences between the unsubstituted and 3,5-dimethyl-substituted derivatives not evident from structural parameters which indicate a reduced access to the metal in the latter. The significance of these data to our understanding of vanadium centers in biological systems is discussed.