Photochemical studies of the alkylammoniun molybdates. Part 5. Photolysis in weak acid solutions

Abstract

Solution photolysis of hexakis(isopropy1ammonium) heptamolybdate(V1) trihydrate, [ NH,Pr'],[Mo702,]*3H20 (l), at pH 5.4 leads to reduction to MoV with involvement of hydroxy-radicals, followed by decomposition to yellow and blue species. Propylene and acetone were detected as oxidation products but quantum yields for their formation were much lower than that for MoV formation. The irradiated single-crystal e.s.r. spectra revealed the formation of MoVO,(OH) in a MOO, octahedral site, which corresponded to the primary event in the solution photolysis. E.s.r. and Raman spectroscopy and flash photolysis were employed to elucidate the mechanism of these reactions.

Complexes with halide and other anions of the molybdenum centre of nitrate reductase from Escherichia coli

“…spectrum of Mo(V) to a single proton, exchangeable with the solvent. The magnitude and the extent of the anisotropy of the coupling of this proton are comparable with those exhibited by a hydroxyl ligand of molybdenum in I Permanent address: National College of Food Technology, University of Reading, Reading RG6 2AP, U.K. irradiated crystals of alkylammonium molybdate (Yamase et al, 1981). This, and additional data on coupling to '10 in sulphite oxidase, make it essentially certain that the proton in the low-pH form of this enzyme, and presumably in the low-pH form of nitrate reductase also, is in the form of a hydroxyl ligand of the metal.…”

Synthesis, crystal structure and photochemistry of Hexakis(butan-1-aminium) heptamolybdate(VI) tetrahydrate

“…The net result of the H-bonding interaction is the organization of cations and anions in alternating layers with lattice water serving as links between the two layers ( Figure S2). In a very early study, Yamase 30,31 explained the mechanism of photoredox process in alkylammonium heptamolybdates revealing the importance of H-bonding interactions. Like several other organic heptamolybdates, the title compound 1 also exhibits photochromism (vide infra).…”

“…24 28 The heptamolybdates (Table 1) in which organic ammonium cations charge balance the [Mo 7 O 24 ] 6− ion exhibit interesting photochemistry. 10,11,13,25,30,31 A survey of the reported synthetic protocols reveals that heptamolybdates are synthesized by a direct reaction of the commercially available (NH 4 ) 6 [Mo 7 O 24 ]•4H 2 O or MoO 3 with an organic amine or an appropriate metal containing reagent. Although some syntheses were performed under hydrothermal conditions 12…”

Aerobic Photooxidation in Water by Polyoxotungstates: The Case of Uracil

“…[12] Especially in aqueous solution, the production of highly reactive hydroxyl radicals OH · from the solvent activation routine, might override more selective pathways, originating within the substrate activation cycle, by interaction with the POM photocatalyst. [10,25,26] The intervention of OH · as the dominant oxidant during photocatalysis in water, is a matter of current debate, substantiated by ESR experiments, [27] product distribution and kinetic studies. [22] The existence of POM-substrate coordination equilibria preceding the oxidation step has been evidenced by NMR experiments, kinetic and selectivity studies using radical scavenger probes.…”