A. B. Venediktov

Synthesis and Structure of Binary Complexes of Platinum Group Metals — Precursors of Metallic Materials

This paper reviews the results of structural studies of binary complexes whose cationic part contains cobalt, rhodium, iridium, ruthenium, and chromium chloropentammne. The structure of these compounds is discussed in the light of the design of new multicomponent precursor compounds. Data are given on the chemical and phase compositions of the polymetallic powders resulting from the thermal decomposition of the compounds studied.

Photochemistry of IrCl62− complex in alcohol solutions

Abstract Both stationary and laser flash photolysis were used to study the photochemistry of IrCl 6 2− in alcohol solutions. The primary photochemical photolysis process at 308 nm was demonstrated to involve electron transfer from the solvent to the excited complex. When the photolysis was performed at 248 nm, the photodissociation of the excited complex, with the elimination of a chlorine atom from the coordination sphere of iridium, was accompanied by electron transfer. At room temperature, the rate constants of the reaction between the primary alcohol radicals and the IrCl 6 2− complex were determined to be (3.2±0.1) × 10 9 M −1 s −1 for hydroxymethyl and (2.3±0.1) × 10 9 M −1 s −1 for α-hydroxyethyl radicals. The dark reactions of the IrCl 6 2− complex arising from photolysis are discussed.

Photochemistry of the IrCl2−6 complex in methanol matrices

Abstract Low-temperature spectrophotometry and electron spin resonance (ESR) were used to study the IrC 2− 6 photochemistry in methanol matrices frozen at 77 K. Photoreaction gives rise to the absorption band of an IrCl 3− 6 complex with a maximum at 215 nm and to a new band with a maximum at 287 nm that is unobservable during IrCl 2− 6 photolysis in solutions at room temperature. The appearance of this new band is assigned to the formation of a weak complex between the . CH 2 OH radical and IrCl 3− 6 ion (i.e. a IrCl 3− 6 … . CH 2 OH radical complex). The irradiation of methanol matrix with IrCl 2− 6 gives rise to the . CH 2 OH radical signal in the ESR spectrum with additional splitting which can be attributed to the partial delocalization of spin density from radical to the IrCl 3− 6 complex and the appearance of hyperfine splitting (HFS) on the iridium nucleus. When the matrix is heated to 115 K the IrCl 3− 6 … . CH 2 OH complex disappears.

On preparation of platinum(IV) nitrate solutions from hexahydroxoplatinates(IV)

The parameters of the processes underlying the current technology of preparation of a Pt(NO3)4 solution were studied and optimized. The basic problems of the process scheme were determined, including limited storage time of solid hexahydroxoplatinum (IV) acid. Approaches were suggested for increasing the yield and the storage time of intermediate products and for simplifying the conditioning scheme of platinum (IV) nitrate with a significant reduction of time and energy costs.

Double complex salts [M(NH3)5Cl][M′Br4] (M = Rh, Ir, Co, Cr, Ru; M′ = Pt, Pd): Synthesis, x-ray diffraction characterization, and thermal properties

Double complex salts (DCSs) with [M(NH3)5Cl]2+ (M = Rh, Ir, Co, Cr, Ru) cations and [PtBr4]2− anions were prepared in high yields. The salts were two-phase mixtures of the anhydrous and monohydro DCSs. Anhydrous analogues containing [PdBr4]2− anions with M = Cr or Ru were synthesized. All the compounds were characterized using a set of physicochemical methods. The crystal structure of chloropentaamminechromium(III) tetrabromopalladate(II) was solved: space group Pnma, Z = 4, a = 17.068(2) Å, b = 8.315(12) Å, c = 9.653(14) Å. The [M(NH3)5Cl][M′X4] (M = Rh, Ir, Co, Cr, Ru; M′ = Pd, Pt; X = Cl, Br) compounds were shown to be isostructural. The [M(NH3)5Cl][PtBr4] · H2O monohydrates are isostructural to the [M(NH3)5Cl][PdCl4] · H2O monohydrates (space group P21/c, z = 4). The properties of the compounds were comparatively analyzed. The tendencies of the thermal stability of the complexes were elucidated. The thermolysis products of the double complex salts obtained under a helium or hydrogen atmosphere were studied.

Photolysis of [PtBr6]2- complex in frozen methanol matrix

Photochemistry of the [PtBr6]2– complex in the low-temperature methanol matrix (77 K) was studied by low-temperature spectrophotometry and ESR spectroscopy. The [PtBr4]2– complex is the main photolysis product. The mechanism of two-electron reduction of the platinum(IV) ion is proposed. The primary photochemical process is electron transfer from the solvent molecule to the photoexcited initial complex to form the intermediate radical complex ([PtBr6]3–...·CH2OH). The transfer of the second electron in the radical complex produces the final reaction products.

[Pd(NH3)4][Ir0.5Os0.5Cl6] Solid Solution: Synthesis and Properties

Abstract[Pd(NH3)4][Ir0.5Os0.5Cl6] solid solution, isomorphic to [Pd(NH3)4][IrCl6], is synthesized and studied by X-ray powder diffraction and elemental analyses, IR and Raman spectroscopies.

Complex rhodium(III) salts with isonicotinic acid: Synthesis and study

A method for the synthesis of complex rhodium(III) salts of the trans-dichlorotetramine series with isonicotinic acid (iso-NicH) was developed. Three new compounds were isolated: [Rh(iso-NicH)3(iso-Nic)Cl2] (I), [Rh(iso-NicH)4Cl2]Cl · 4H2O (II), and Na3[Rh(iso-Nic)4Cl2] · 9H2O (III). The compounds synthesized were characterized by elemental analysis, X-ray phase analysis, and IR spectroscopy. The crystal structures of salts II and III were determined by X-ray diffraction analysis. The thermal properties of all compounds were studied by the DTA method. The intermediate and final thermolysis products were isolated and characterized.

Properties of nitric acid palladium solutions with a high metal concentration

Nitric acid solutions (cPd up to 3.2 M) with variable HNO3 concentration were studied by electronic spectroscopy, 14N and 17O NMR, acid-base titration, gravimetry, and other methods. Solid phases that precipitated on storing these solutions were studied by X-ray phase analysis, thermogravimetry, and IR spectroscopy. The conditions for stability of particular Pd(II) species were determined, and specific features of aging of such highly concentrated palladium solutions were revealed. A procedure for palladium isolation as [Pd(NH3)4](NO3)2 from nitric acid solutions in 98% yield was developed.

[Zn(NH3)4][PtCl6] and [Cd(NH3)4][PtCl6] as precursors for intermetallic compounds PtZn and PtCd

Double complex salts (tetraamminezinc and tetraamminecadmium hexachloroplatinates) have been synthesized. Their thermal properties have been studied, as well as the products of their degradation in hydrogen and helium atmospheres. Optimal thermolysis schedules have been determined. Thermolysis under hydrogen yields intermetallic compounds PtZn and PtCd.