Equilibria and dynamics of some aqueous peroxomolybdate catalysts: a 17O NMR spectroscopic study

Abstract

The equilibrium speciation at 278 K and the dynamics in the systems) and 0.6 M Na(Cl) medium has been determined from 17 O NMR integral and shift data in the range 0.7 ≤ pH ≤ 4.1 and at excess of peroxide ([H 2 O 2 ] tot /[Mo] tot = 3). In 0.3 M Na 2 (SO 4 ) medium species with the following compositions were found:(2,2,6,0), where (Mo) corresponds to MoO 4 2Ϫ , (X) to O 2 2Ϫ or HOO Ϫ and (S) to SO 4 2Ϫ . In 0.6 M Na(Cl) medium the diperoxomolybdosulfate complex MoX 2 S Ϫ is replaced with a novel diperoxomolybdochloride complex MoX 2 Cl Ϫ (2,1,2,1), where (Cl) corresponds to Cl Ϫ . The numbers in parentheses refer to the values of p,q,r and s in the formula above. The stoichiometries of each complex are given by the abbreviated formula Mo q X r S s (2q ϩ 2s Ϫ p)and Mo q X r Cl s (2q ϩ s Ϫ p)-. The following formation constants with 3σ were obtained with values for 0.6 M Na(Cl) in parenthesis: log

Peroxomolybdate(vi)–citrate and –malate complex interconversions by pH-dependence. Synthetic, structural and spectroscopic studies

“…A variety of peroxomolybdates coordinated with oxygen and nitrogen donors have been characterized structurally, [21][22][23][24][25][26][27][28][29][30][31][32] and studied in solution and the solid state. [33][34][35][36][37][38][39] For good reasons hydroxycarboxylic acids are frequently used as active coordinating agents; they exist widely in biological media, and have been known to influence strategic metabolic pathways governing the physiological activities of cells and multicellular organisms. Indeed, some peroxomolybdates() carrying a hydroxycarboxylate ligand have been reported; they include monomeric citrate and glycolate complexes, K 43 Citrate ions are omnipresent small molecules in most plants and animal tissues where they regulate fundamental physiological processes, and are intermediates in carbohydrate metabolism, e.g.…”

17O NMR study of aqueous peroxoisopolymolybdate equilibria at lower peroxide/Mo ratiosElectronic supplementary information (ESI) available: concentrations of total Mo, total H2O2 and other species expressed as [Mo]. See http://www.rsc.org/suppdata/dt/b2/b206396b/

“…Also the few existing studies in aqueous solution have been within limited ranges of pH and peroxide concentration, with an emphasis on the use of excess peroxide. 10, 11 The speciation when peroxide is not in excess has remained poorly understood. The most incisive methods currently available for a solution study are 17 O NMR and potentiometry.…”

Cyclohexanone Oxidation over H3PMo12O40 Heteropolyacid via Two Activation Modes Microwave Irradiation and Conventional Method

“…In the second step, H2O2 intervenes to oxidize simultaneously the reduced phase of the POM and to form peroxospecies (oxidized peroxo-POMox). It has been reported in several studies that transition elements with high oxidation states (V(V), Nb(V), Mo(VI), and W(VI)) have a high affinity towards H2O2 [31][32][33][34][35]. This has as for consequence the formation of peroxocomplexes highlighted by several techniques (X-ray diffraction, FTIR, and Raman spectroscopies).…”