Министерство науки и высшего образования Российской Федерации Российская академия наук Научный совет по неорганической химии РАН Научный совет по аналитической химии РАН Научный совет по химической технологии РАН Российское химическое общество имени Д.И

Solid-state transformations of a 3[Pd(NH3)4]Cl2 + (NH4)2CrO4 mixture at temperatures from 40 to 550°C in various media have been studied by thermal analysis and mass spectrometry. The results demonstrate that the solid thermolysis product obtained in an argon atmosphere consists of a single phase: palladium-based Pd1 – xCrx solid solution isostructural with palladium and having a unit-cell parameter a = 3.897(2) Å. Its formation proceeds through the formation of metallic Pd and Cr, as evidenced by the absence of chromium oxide phases in all of the solid intermediate thermolysis products. The solid thermolysis product obtained in air consists of the phases Pd and PdO. A model has been proposed for the transformations of the 3[Pd(NH3)4]Cl2 + (NH4)2CrO4 mixture through the formation of metallic palladium and chromium.

Thermal transformations of 3[Pt(NH3)4]Cl2–(NH4)2CrO4 (I) and 3[Pt(NH3)4]Cl2–2(NH4)2Cr2O7 (II) mixtures in a solid state have been studied by thermal analysis and mass spectrometry in an inert (Ar) atmosphere and air at temperatures from 40 to 550°C. The chemical and phase compositions of the thermolysis products obtained in argon have been determined: Pt and Cr2O3 in mixture I and Pt, a platinum-based Pt1 – y Cr y solid solution, and Cr2O3 in mixture II. The thermal transformation products of mixtures I and II in air consist of two phases: Pt and Cr2O3. It has been shown that interactions in the mixtures proceed through the formation of a metallic chromium phase. The materials obtained in this study can find application as catalysts for low-temperature fuel cells, as well as for organic synthesis processes.

A solid product formed during thermolysis of tetraammineplatinum(II) chloride and ammonium heptamolybdate in an aqueous alkaline solution under autoclaving conditions has been studied by means of dynamic light scattering, scanning electron microscopy, X-ray diffraction analysis, and elemental analysis. The amount of free ammonia formed in the reaction has been determined by titration. The pathway of platinum(II) and heptamolybdate ions reduction by inner-sphere ammonium into the corresponding metals has been proposed.

A solid product formed during thermolysis of tetraammineplatinum(II) chloride and ammonium heptamolybdate in an aqueous alkaline solution under autoclaving conditions has been studied by means of dynamic light scattering, scanning electron microscopy, X-ray diffraction analysis, and elemental analysis. The amount of free ammonia formed in the reaction has been determined by titration. The pathway of platinum(II) and heptamolybdate ions reduction by inner-sphere ammonium into the corresponding metals has been proposed.

Представлена методология уточнения кристаллической структуры силленитов номинального состава Bi24M2O40, основанная на выборе корректных исходной модели и тепловых параметров атомов. Работоспособность предложенной методики показана на примере кристаллов с M = Si, Fe, V, для которых найден реальный состав с учетом состава каждой кристаллографической позиции структуры. Отдельные детали структуры подтверждены ИК- и КРС-спектроскопией.

A methodology for refining the crystal structure of sillenites of nominal composition Bi 24 M 2 O 40 based on the choice of the correct initial model and thermal atomic parameters is reported. The validity of the approach proposed is demonstrated by examples of crystals with M = Si, Fe, or V, for which the real composition is found with allowance for the composition of each structural site. Individual structural details are confirmed by IR and Raman spectroscopy data.

It is shown that the real composition and structure of phases belonging to the sillenite family can be determined using a complex of techniques (diffraction methods, vibrational and X-ray absorption spectroscopy, and electron probe X-ray microanalysis) with a subsequent crystal-chemical analysis of the data. Refined compositions are presented for phases of nominal composition Bi 24 M 2 O 40 with M = Zn 2+ , Al 3+ , Ga 3+ , Fe 3+ , Si 4+ , Ti 4+ , Mn 4+ , and P 5+ , which demonstrate types and concentrations of point defects as functions of the M type.

Показано, что определение реального состава и строения фаз семейства силленита возможно при использовании комплекса методов (дифракционные методы, колебательная и рентгеноабсорбционная спектроскопия, рентгеноспектральный микроанализ) с последующим кристаллохимическим анализом полученных данных. Для фаз номинального состава Bi24M2O40 с M = Zn2+, Al3+, Ga3+, Fe3+, Si4+, Ti4+, Mn4+, P5+ представлены уточненные составы, демонстрирующие типы и концентрации точечных дефектов в зависимости от вида M.

In the Bi2O3-SiO2-VO25+O5 system, single crystal solid solutions of the sillenite family of the general composition Bi-24(Bi,Si,V)(2)O-40 are obtained by a hydrothermal method and for the first time characterized by neutron and X-ray diffraction analysis. The tetrahedral position is found to contain vanadium ions with different formal charges (V4+ and V5+) responsible for green and orange colors, respectively, of the samples. For the first time, for some sillenites of this system dissymmetrization of the structure (a transition from the I23 space group into P23) is revealed, which is caused by the presence of several atoms in one crystallographic position and also by crystal growth conditions.

X-ray diffraction studies of sillenite Bi24V2O40 single crystals grown by the hydrothermal method are performed for a separate crystal and powdered crystals. It is found that the composition of the two specimens is described by the (Bi24 − x ▭ x )[Bi y 3+ V 1−y 5+ ]2 O40 general formula with completely populated oxygen sites but differs in the content of vacancies at the bismuth site (this was established for the first time) and the Bi: V ratio at the tetrahedral site. The structural models of all the vanadium-containing sillenites reported in the literature are considered, and the possibility that Bi atoms are located at the centers of BiO4 tetrahedra is established.

In the Bi 2 O 3 -SiO 2 -V 2 5+ +O 5 system, single crystal solid solutions of the sillenite family of the general composition Bi 24 (Bi,Si,V) 2 O 40 are obtained by a hydrothermal method and for the first time characterized by neutron and X-ray diffraction analysis. The tetrahedral position is found to contain vanadium ions with different formal charges (V 4+ and V 5+ ) responsible for green and orange colors, respectively, of the samples. For the first time, for some sillenites of this system dissymmetrization of the structure (a transition from the I 23 space group into P 23) is revealed, which is caused by the presence of several atoms in one crystallographic position and also by crystal growth conditions.

Выполнено рентгеноструктурное исследование монокристаллов силленита Bi24V2O40, выращенных гидротермальным методом, как в виде отдельного кристалла, так и измельченных в порошок кристаллов. Обнаружено, что их состав может быть описан общей формулой (Bi24 - x x)[Bi V ]2O40, но с разным содержанием вакансий в позиции висмута (выявлено впервые), отсутствием кислородных вакансий и разным соотношением Bi и V в тетраэдрической позиции. Рассмотрены все известные в литературе модели строения ванадийсодержащих силленитов и установлена принципиальная возможность нахождения атомов Bi в центре тетраэдра BiO4.

A precise X-ray diffraction study of a sillenite crystal with the initial composition Bi24(Si x Mn1−x )2O40 grown by the hydrothermal method showed the presence of diffraction reflections that make it possible to assign this crystal to the sp. gr. P23, in contrast to the Bi24Si2O40 crystal with the sp. gr. I23. The distribution of cations over the two positions of the crystal structure of the general composition Bi24(Bi0.130(3)Si0.277(3)Mn1.593(3))O40 with three atoms (Bi, Si, Mn) in one position of the sp. gr. P 23 is established. The disymmetrization of the Bi24(Bi, Si, Mn)2O40 crystal is explained by the kinetic order-disorder phase transition, which is caused by the presence of several atoms with different crystallochemical properties in one crystallographic position of the structure, in contrast to the Bi24Si2O40 crystal, where this phenomenon is absent.

The crystal structures of general composition nBi(2)O(3)-mB(2)O(3) were analyzed and systematized with the use of the structures of borate groups. Based on the CNs calculated by the bond valence method, the shapes of bismuth coordination polyhedra derived from an octahedron were suggested. A correlation was found between the number of BO3 triangles and BO4 tetrahedra in borate groups, the average CN of Bi atoms, and the degree of distortion of Bi polyhedra as a function of the m : n ratio, as well as between the polarity of BO4 tetrahedra and noncentrosymmetry of the structures. The role of Bi3+ with the active E pair in the manifestation of specific features of the forms of bismuth polyhedra and the types of connection of boron polyhedra was elucidated.