Applications of molybdenum-95 N.M.R. spectroscopy. X. Polyoxomolybdates

Abstract

An initial survey of the 95Mo n.m.r. properties of a range of 12 polyoxomolybdates is presented. The species resonate in the range - 18 to + 140 ppm. The observed line widths generally exceed 100 Hz for six-coordinate molybdenum sites of low symmetry, but can be narrow (< 20 Hz at 20�) for four-coordinate sites. Aqueous solutions of [Mo7O24]6- at pH 6.1 exhibit exchange between Mo- and Mo7-based species. Solutions of α-[Mo8O26]4- in MeCN feature a single narrow resonance (δ16, Wh/2 23 Hz at 20�) assigned to the tetrahedral capping sites, while two broad resonances (δ19, Wh/2 240 Hz; δ109, Wh/2 C. 270 HZ) are seen in equivalent solutions of β-[Mo8O26]4-. In the cases cited above, 17O n.m.r. is used to confirm the integrity of sample solutions and assists in correction of the 95Mo n.m.r. properties of β-[Mo8O26]4 reported in a previous communication.

The formation of an active component in V-Mo-Nb-O catalysts of ethane oxidation and ammoxidation

“…1a, spectrum 4) and lines that are typical of β-Mo 8 O 26 4- [8], but slightly shifted (Fig. 1a, spectrum 3).…”

Oxocomplexes of Mo(vi) and W(vi) with 8-hydroxyquinoline-5-sulfonate in solution: structural studies and the effect of the metal ion on the photophysical behaviour

“…6,[8][9][10] The 95 Mo and 183 W signals of the most important polyoxometalates have previously been assigned, in particular for M 7 O 24 6− (M = W, Mo), the predominant species at acidic pH values. [75][76][77] Polyoxotungstates give rise to sharp 183 W signals, but 95 Mo signals of polyoxomolybdates are generally broadened, which makes it difficult to detect and, in particular, to quantify them in solution.…”

NMR Spectroscopic Studies of Interactions in Solution during the Synthesis of MoVTeNb Oxide Catalysts

“…The synthesis of Na 6 TeMo 6 O 24 ·xH 2 O was carried out according to the method of Filowitz et al [17] The product composition and its purity were confirmed by elemental analysis and the 17 O and 95 Mo NMR spectra. [17,18] NMR spectra were measured with a Bruker Avance-400 spectrometer, at the natural content of 125 Te, 17 O, and 95 Mo (≈ 7, 0.04, and 16 %, respectively). The 125 Te chemical shifts (δ) given relative to Me 2 Te were determined by using telluric acid aqueous solution as a secondary external standard (δ = 707 ppm).…”

“…With this aim in mind, we have applied multinuclear NMR spectroscopy, as it is the most informative technique for studying speciation of POMs in solutions. [16][17][18] …”