Mo 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 [Mo₆O₁₉)]^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) Å; V = 7478.1 (12) ų; Z = 4; structure solutions and refinement based on 3534 reflections (F₀3σ(F₀)) converged at R = 0.059.