Abstract

A series of aryldiazenido compounds of the type (nBu 4N) 3[Mo 6O 18(N 2Ar)] have been prepared by treatment of (nBu 4N) 4[Mo 8O 26] 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 95Mo and 17O NMR spectroscopy in acetonitrile. Their spectra indicate C 4v symmetry, and hence stereochemical nonrigidity in solution. The 95Mo chemical shifts are mainly determined by variation in the paramagnetic shielding term, ? para. The strongly deshielded resonance of the Mo II centre spans a large range (600-1100 ppm). © Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.