Lindqvist-type (aryldiazenido)polyoxomolybdates -: Synthesis, and structural and spectroscopic characterization of compounds of the type (nBu4N)3[Mo6O18(N2Ar)]

A series of aryldiazenido compounds of the type (nBu(4)N)(3)-[Mo6O18(N2Ar)] have been prepared by treatment of (nBu(4)N)(4)-[Mo8O26] with the appropriate arylhydrazines in acetonitrile or in methanol. All these compounds are isostructural. Two members of the series, the o-nitro and the p-carboxy derivatives, have been characterized by single-crystal X-ray diffraction. The aryl ring in the first anion lies in a mirror plane of the polyoxometalate, while in the second one it is tilted, allowing hydrogen bonding between the carboxylic acid function and a neighbouring anion. The aryldiazenido ligands exhibit the characteristic features of the singly bent coordination mode with short Mo-N and N-N bond lengths indicative of multiple bond character. The compounds have been characterized by Mo-95 and O-17 NMR spectroscopy in acetonitrile. Their spectra indicate C-4nu symmetry, and hence stereochemical nonrigidity in solution. The Mo-95 chemical shifts are mainly determined by variation in the paramagnetic shielding term, sigma(para). The strongly deshielded resonance of the Mo-II centre spans a large range (600-1100 ppm). (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.