REDOX-RESPONSIVE MOLYBDENUM MONONITROSYL COMPLEXES INCORPORATING CYCLIC POLYETHER CATION BINDING-SITES AND X-RAY CRYSTAL-STRUCTURE OF [MO(NO)(HB(3,5-ME2C3N2H)3)(OCH2(CH2OCH2)3CH2O)]

The complexes [Mo(NO){HB(Me2pz)3}{OCH2(CH2OCH2)nCH2O}] (n = 2-5; HB(Me2pz)3- = hydrotris(3,5-dimethylpyrazolyl)borate) have been synthesized and characterized by spectroscopic methods. All contain the redox-active {Mo(NO)}3+ moiety incorporated in an unusually large chelate ring which forms a cyclic polyether structure. Cyclic voltammetric studies of these compounds reveal a reduction process at ca. -1.3 V (SCE) which is shifted to more anodic potentials in the presence of an equimolar concentration of sodium ions. At higher concentrations, decomposition is associated with the reduction process. In the case where n = 3, 1:1 complexes with Li+, Na+, and K+ have been isolated. The molecular structure of [Mo(NO){HB-(Me2pz)3}{OCH2(CH2OCH2)3CH2O}] has been determined by X-ray diffraction methods. The compound crystallizes in the orthorhombic space group Pbca (No. 61) with eight molecules in a cell of dimensions a = 16.937 (3), b = 15.143 (4), and c = 22.034 (8) angstrom. Full-matrix least-squares refinement gives final R, R(w) on F of 0.051, 0.079 for 3063 observed [F > 5-sigma(F)] data. This structure confirms the presence of a 14-membered chelate ring (Mo-O = 1.903 (4) and 1.910 (4) angstrom; O-Mo-O = 101.0 (2)-degrees) and a linear nitric oxide ligand (Mo-N-O = 177.9 (5)-degrees; N-O = 1.190 (6) angstrom). The cyclic polyether ring is extended away from the bulky HB(Me2pz)3 ligand.