Sol-gel chemistry of transition metal oxides

http://alpha.chem.umb.edu/chemistry/ch611/documents/C-Htransitionmetalbonds.pdf

Carbonhydrogen-transition metal bonds

Transition metal complexes containing organoimido (nr) and related ligands

Binuclear oxo-bridged iron(iii) complexes

Zirconia-supported tungsten oxide catalysts were prepared by suspending hydrous zirconium oxide in aqueous solutions of ammonium metatungstate at their natural pH. The suspensions were refluxed at 383 K followed by evaporation of the water, drying and calcination. The WO3 loadings were chosen between 3.6 and 32 wt % and the calcination temperatures were in the range 773 ≤ T ≤ 1273 K. The resulting materials were structurally characterized by X-ray diffraction, differential thermal analysis, and surface area measurements, by laser Raman and Fourier transform infrared (FTIR) spectroscopy, and by UV−vis diffuse reflectance spectroscopy. Their acidic properties were tested by FTIR spectroscopy using carbon monoxide as a probe molecule. The experimental results indicate that the presence of WOx retards the crystallization of the zirconia material and stabilizes the tetragonal ZrO2 phase and the intrinsic BET surface area. W−O−W linkages are detected even at the lowest WO3 loadings indicating that oligomeric WO...

Genesis and Structure of WOx/ZrO2 Solid Acid Catalysts†

Transition metal oxo complexes

Transition metal nitrido complexes

Osmium tetroxide reacts with mono-alkenes (R) to give five-co-ordinate mono- or di-esters of the saturated diolato-ligand (O2R)2–, viz. [Os2O4(O2R)2](I) and [OsO(O2R)2](II); (II) may also be obtained by the reaction of OsO4 with the glycol R(OH)2. With alkenes (R) or acetylene in the presence of tertiary nitrogen bases, L, the octahedral ‘osmyl’ species [OsO2L2(O2R)](III) and [Os2O4L4(O4C2H2)](IV) are formed. Spectroscopic and other data are used to assign structures to these complexes; 18O and 2H substitution has been used to help the interpretation of i.r. data.

Reaction of osmium tetroxide with alkenes, glycols, and alkynes; oxo-osmium(VI) esters and their structures

unsaturated tissue components by osmium tetroxide (Os0 ) is generally believed to involve the initial formation of cyclic osmium(VI) monoon diesters (9) (and reactions with protein in some cases (8)). Howeven, it has recently been proposed (7) that most of the 0504 simply attaches itself by hydrogen bonds to aliphatic side chains and proteins in the tissue. It is, however, very unlikely on chemical grounds that 0504 would form hydrogen bonds: the oxo ligands have insufficient residual orbital electron density to form hydrogen bonds owing to the considerable (ti + r) electron delocalization to the central osmium(VIII) atom. In this note we show, by repeating Litman and Bannett’s experiments (7) with “model” osmium(VI) esters of known structures and stoichiometnies (3-5), that their observations may be equally well explained by the conventional osmium(VI) ester formation theory of tissue staining. We also provide direct experimental evidence that 0s0 has negligible hydrogenbonding properties.

William P. Griffith

Papers

Transition metal oxo complexes

Transition metal nitrido complexes

Reaction of osmium tetroxide with alkenes, glycols, and alkynes; oxo-osmium(VI) esters and their structures

Mechanism of tissue component staining by osmium tetroxide

Heptacyano complexes of rhenium(III) and molybdenum(II)