Transition metal oxo complexes

Spectroscopic studies of the molybdenum-containing dimethyl sulfoxide reductase from Rhodobacter sphaeroides f. sp. denitrificans.

The Coordination and Bioinorganic Chemistry of Molybdenum

We report for the first time the synthesis of monoclinic WO3 quantum dots. A solvothermal processing at 250 °C in oleic acid of W chloroalkoxide solutions was employed. It was shown that the bulk monoclinic crystallographic phase is the stable one even for the nanosized regime (mean size 4 nm). The nanocrystals were characterized by X-ray diffraction, High resolution transmission electron microscopy, X-ray photoelectron spectroscopy, UV–vis, Fourier transform infrared and Raman spectroscopy. It was concluded that they were constituted by a core of monoclinic WO3, surface covered by unstable W(V) species, slowly oxidized upon standing in room conditions. The WO3 nanocrystals could be easily processed to prepare gas-sensing devices, without any phase transition up to at least 500 °C. The devices displayed remarkable response to both oxidizing (nitrogen dioxide) and reducing (ethanol) gases in concentrations ranging from 1 to 5 ppm and from 100 to 500 ppm, at low operating temperatures of 100 and 200 °C, res...

Solvothermal, Chloroalkoxide-based Synthesis of Monoclinic WO3 Quantum Dots and Gas-Sensing Enhancement by Surface Oxygen Vacancies

A series of oxomolybdate(v) complexes with methanol was prepared by the reaction of (PyH) 5 [MoOCl 4 (H 2 O)] 3 Cl 2 (1) or (PyH)[MoOBr 4 ] (PyH + = pyridinium cation, C 5 H 5 NH + ) in methanol. (PyH) 2 [MoOCl 4 (MeOH)]Cl (2) is obtained upon substitution of coordinated water for methanol in 1. Small amounts of weak bases such as pyridine or trifluoroacetate promote further substitution chemistry at the labile sites, followed by dimerisation to the well-known {Mo 2 O 4 } 2 + core. A dinuclear anion with coordinated methanol can be isolated as its pyridinium salt, (PyH) 2 [Mo 2 O 4 Cl 4 (MeOH) 2 ], in two crystalline modifications, either as a triclinic (3) or as an orthorhombic polymorph (4). After prolonged reaction times further assembly of dinuclear fragments takes place and tetranuclear [Mo 4 O 8 (OMe) 2 (MeOH) 2 Cl 4 ] 2 - is formed. The products of the analogous reactions with (PyH)[MoOBr 4 ] as the starting material depend largely upon the reaction temperature. Dinuclear (PyH) 2 [Mo 2 O 4 Br 4 (MeOH) 2 ] (5), which crystallises in an orthorhombic unit cell and whose structure is isotypic to that of 4, is obtained only if the reaction takes place at low temperature (5 °C); under ambient conditions (PyH) 2 (Mo 4 O 8 (OMe) 2 -(MeOH) 2 Br 4 ] (6) is obtained instead. The tetranuclear anion of 6 consists of a commonly adopted assembly of two {Mo 2 O 4 } 2 + units. The identity of the products was determined by infrared spectroscopy and X-ray structure analyses.

Novel Methanol-Containing Oxomolybdate(V) Complexes: Synthesis and Structural Characterisation of Intermediates in the Formation of {Mo2O4}2+ Clusters from [MoOCl4(H2O)]– and [MoOBr4]– Precursors

E. A. Allen

Papers

890. Halide and oxyhalide complexes of molybdenum and tungsten