B. N. Novgorodov

First trigonal-antiprismatic tris-dichloroglyoximate iron(II) clathrochelate and its reactivity in nucleophilic substitution reactions

Tris-dichloroglyoximate clathrochelate [Fe(Cl2Gm)3(SnCl3)2]2− dianion has been synthesized by a procedure differing from those described earlier for boron-capped analogs. The co-ordinately saturated SnCl62− dianion is now used as the capping agent instead of boron-containing Lewis acids. The tris-dichloroglyoximate tin-capped product obtained is far less reactive than its boron-capped analogs, and only in the case of a thiophenolate anion was the “regular” hexafunctionalized clathrochelate obtained. The complexes synthesized have been characterized by elemental analysis, PD and MALDI-TOF mass, IR, UV-vis and 1H, 13C and 119Sn NMR spectra, cyclic voltammetry, and X-ray crystallography for the clathrochelate [Fe(Cl2Gm)3(SnCl3)2]2− dianion. The geometry of the functionalized complex (the distortion angle φ and main bond lengths in the clathrochelate framework) has been deduced from the quadrupole splitting value in the 57Fe Mossbauer spectrum and EXAFS data, respectively.

Structure of polynuclear palladium(ii) hydroxocomplexes formed upon alkaline hydrolysis of palladium(ii) chloride complexes

The structure of polynuclear PdII hydroxocomplexes (PHC) formed as a result of alkaline hydrolysis of PdII chloride complexes was studied by EXAFS, SAXS, and TEM methods. It is established that in aqueous solutions a hydroxocomplex particle is a filament curled into a ball containing about 100 Pd atoms. The filament consists of planar coordination squares of PdO4 units linkedvia one or two oxygen bridges of different geometry. Aging of samples results in an increase in the number of single bridging ligands and a decrease in the diameter of particles. Interatomic distances around palladium atoms were determined.

Nanocomposites Based Upon Alumina and Zirconia Pillared Clays Loaded with Transition Metal Cations and Clusters of Precious Metals: Synthesis, Properties and Catalysis of NO x Selective Reduction by Hydrocarbons

Thermally stable alumina and zirconia pillared clays loaded with copper and cobalt cations and silver nanoparticles were synthesized. The structural and surface features of these nanosystems were studied and compared with those of bulk analogs -partially stabilized zirconias and γ-alumina loaded with the same active components. Specificity of the catalytic properties of nanocomposites in the reactions of nitrogen oxides reduction by propane, propylene and decane in the excess of oxygen appears to be determined both by the degree of interaction between pillars and active components and the type of reducing agent.

The effect of supports (Al2O3, Al2O3-CeO2 and Al2O3-CeZrO2) on the nature of gold-species in supported gold catalysts

This work is concerned with the study of Au specimens produced by gold deposition on nanosized mixed oxides (alumina, ceria, zirconia) prepared by the sol-gel method using organometallic precursors. According to X-ray absorption near edge structure, extended X-ray absorption fine structure, transmission electron microscopy data, and ultraviolet-visible and X-ray photoelectron spectroscopy measurements, mixed Al-Ce-Zr oxides are quite effective for stabilization of different gold specimens. The samples pre- treated in hydrogen at 150°C are characterized by the presence of gold Au3+ cations located on the surface in slightly disordered octahedral oxygen coordination. Metallic gold nanoparticles with a size of about 2 nm and gold clusters were found in the samples treated in hydrogen at 300°C.

Polymeric low-valence platinum-phenanthroline complexes as precursors of platinum colloids

It was found that the reduction of Pt(II), Pt(III) and Pt(I,III) acetates with H2 in the presence of 1,10-phenanthroline (phen), according to the standard procedure for the synthesis of palladium-561 giant clusters, resulted, unexpectedly, in the high-nuclear Pt(I) complex of the empirical composition Pt8phen3(OAc)4(OH)4(H2O)6 instead of the expected platinum colloid. Data of electron microscopy (TEM, HREM), small-angle X-ray scattering (SAXS), EXAFS and thermal analysis (DTA-TG) combined with elemental microanalysis all point to a loose structure of the obtained complex, with a minor PtPt bonding (average coordination number for the PtPt bonds is about 1). Variation of the preparation procedure resulted in a series of polymeric phen-platinum complexes, containing Pt atoms in oxidation states ranging from (+1) to (+0.3), and whose main structural features were established by the above-mentioned techniques. Giant clusters with dense PtPtOx cores (coordination number for the PtPt bonds is about 6) were obtained by gradual heating of the precursor Pt complex to about 200°C as well as by a modified preparation procedure at 20°C.

Determination of the local structure of a highly dispersed Pd-Nanosystem located on a titanium dioxide carrier

This work is devoted to a structural study of a highly dispersed Pd nanosystem, which is stabilized in the TiO2 matrix, by XAFS spectroscopy. Nanocomposite was prepared from bimetallic PdCo(μ-OOCMe)4(NCMe) precursor followed by processing in several ways: calcination in air and in argon and microwave irradiation. The local structure of Pd catalysts formed by different methods was studied. Possible structural models were considered in detail.

EXAFS study of ultradisperse noble metal nanoparticles structure phase conversion

Abstract The structure and its difference from bulk metals was studied for nanoparticles of Pt and Pd by EXAFS-spectroscopy. These particles were obtained by different methods and from different precursors. The measurements have been conducted to investigate the process of phase transition under thermal relaxation and reagents adsorption. It was shown for Pt clusters that the initial structure has form of the polymeric chains which changes on heating to usual bulk metal one.

The application of the atom label method to studying surface structure of the carbon deposited nickel particles by using EXAFS

This work is an effort to use the atom label method for studying surface structure of the carbon deposited nickel particles by EXAFS. All the data show that H2Se may be used as label atoms.

EXAFS study of the ultradispersive metal particle surface structure using inert gases as label atoms

Abstract An experimental apparatus was developed to perform inert gas adsorption in situ. The investigation of Kr adsorption on supported Pd catalysts was carried out by means of EXAFS spectroscopy on K-edges of absorption of Kr and Pd. This study may give important information concerning the surface structure of metal particles and its interaction with adsorbates. This information, in turn, could allow us to understand the mechanism of catalytic reactions and the methods of improving the catalytic activity.