95Mo NMR studies of (aryldiazenido)- and (organohydrazido)molybdates. Crystal and molecular structure of [n-Bu4N]3[Mo6O18(NNC6F5)]

The 95Mo NMR spectroscopy of a select series of (aryldiazenido)- and (organohydrazido)molybdates of known structure has been studied. The chemical shifts, line widths, and in select cases T1 values and the effects of temperature variation are reported. For the most part, with notable exceptions, the expected number of molybdenum signals are observed in the 95Mo NMR spectra although temperature variation may be required to reveal the signals. There is a lack of simple correlation between component structural units in a given compound and some consistent chemical shift value that could be ascribed to that unit. In particular the spectrum for [Mo6O18(NNAr)]3- differs markedly from that of [Mo6O19]2-, although the compounds are the closest structural analogues. Accordingly, the details of the structure, electronic spectrum, and electrochemistry of [Mo6O18(NNAr)]3- are presented. Although the geometry of [Mo6O18(NNAr)]3- is grossly related to that of [Mo6O19]2- by substitution of a diazenido unit for an oxo group, the detailed investigations establish significant differences in the electronic spectra, redox electrochemistry, and structural parameters. Crystal data for [n-Bu4N]3[Mo6O18(NNC6F5)]: orthorhombic space group Pmcn; a = 17.345 (5), b = 17.645 (3), c = 24.434 (7) /angstrom/; V = 7478.1 (12) /angstrom/3; Z = 4; structure solutions and refinement based on 3534 reflections (F/sub o/ />=/ 3σ(F/sub o/)) converged at R = 0.059. 34 references, 11 figures, 8 tables