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 20º) 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, W_h/2 23 Hz at 20º) assigned to the tetrahedral capping sites, while two broad resonances (δ19, W_h/2 240 Hz; δ109, W_h/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.