Showing papers by "Vadim G. Kessler published in 1994"

Reactions of coordinated ligands: topological and stoichiometric control for mixed-metal alkoxides: synthesis and molecular structure of [La{(OC2H4)3N}2{Nb(OPri)4}3]

Abstract: The reaction of lanthanum isopropoxide with 2 equivalents of triethanolamine leads to a novel ‘diatrane’ complex H3La[(OC2H4)3N]2; its reaction with Nb(OPri)5 provides a soluble and volatile mixed-metal species [La{(OC2H4)3N}2{Nb(OPri)4}3] whose molecular structure is based on a central ‘diatrane’ core with eight-coordinate lanthanum while all niobium centres are six-coordinate.

Oxoalkoxides—True precursors of complex oxides

Abstract: X-ray structural analysis of “crystalline alkoxides” in many cases reveals that along with OR-groups their molecules also contain oxo-ligands The following possible reactions leading to formation of oxoalkoxides have been discussed: hydrolysis, pyrolysis (frequently uncontrollable), ether elimination, oxidation of OR-groups (which exist in solutions of alkali, alkaline-earth and rare earth elements), or alkoxides of the lower oxidation states (which are formed by reduction of M(OR)n on cathode during electrolysis or by hydrogen in statu nascendi) Oligomeric oxoalkoxides differ from the polymeric alkoxides M(OR)n in considerably higher solubility and reactivity The most important role of oxoalkoxides in the processes of formation of oxides has been demonstrated using as an example preparation of BaTiO3 from alkoxides

The synthesis, crystal and molecular structures of bimetallic ethoxides of barium and titanium, and calcium and titanium: [M{Ti2(µ3-OEt)2(µ-OEt)3(OEt)4}2](M = Ca, Ba)

Abstract: The X-ray single-crystal studies of [M{Ti2(OR)9}2](M = Ca, Ba; R = Et) obtained from EtOH solutions in 1 : 4 metal–titanium ratios show that these complexes, both in the solid state and in solution, are composed of symmetric molecules, in which the central eight-coordinated metal atom is bound to two face-sharing bioctahedral [Ti2(OR)9] groups.

What are the Molecules of Which the Samples of Metal Alkoxides do Really Consist

Abstract: On the basis of consideration of the properties of AI, In, Ln, Ti, Zr, Hf, NbO3+, MoO4+, WO4+, MoO22+ MO22+, Fe, Co, Ni alkoxide derivatives the main regularities in poly- and oligomerization properties have been deduced 1) The molecular complexity increases in time (aging) and on action of alcohols. This process is followed by the increase in the melting and boiling points, decrease in solubility in ROH and weakening of colour. In the mass-spectra - in connection with the temperature of transition into the gas phase - increases the stability of products with lower molecular masses. 2) oligomerization occurs on dissolution in aromatic hydrocarbons or on a short thermal treatment (melting, distillation). The oligomerization products possess lower thermal constants, higher solubility in ROH and more intense colour. Their mass- spectra are containing the fragments of higher masses corresponding to oligomers existing apparently also in the condensed phase. The mastering of these regularities permits the monitoring of molecular composition and thus physicochemical properties of the samples which are of importance for their technological application. The presence of oxoalkoxides in the “M(OR)n” samples should be taken into consideration on the preparation of solutions used in the synthesis of powders and films of pure simple and mixed oxides.