Stanislav K. Filatov

Anion-centered tetrahedra in inorganic compounds.

Sergey V. Krivovichev,*,†,‡ Olivier Mentre,́ Oleg I. Siidra,† Marie Colmont, and Stanislav K. Filatov† †St. Petersburg State University, Department of Crystallography, University Emb. 7/9, 199034 St. Petersburg, Russia ‡Institute of Silicate Chemistry, Russian Academy of Sciences, Makarova Emb. 6, 199034 St. Petersburg, Russia UCCS, Equipe de Chimie du Solide, UMR CNRS 8181, ENSC LilleUST Lille, BP 90108, 59652 Villeneuve d’Ascq Cedex, France

Minerals and synthetic Pb(II) compounds with oxocentered tetrahedra: review and classification

The crystal structures of minerals and inorganic compounds with OPb4 oxocentered tetrahedra are reviewed. It is shown that the OPb4 tetrahedral units may link by sharing common Pb atoms to form structural units of various shape and dimensionality. These units determine basic topology of the structures and influence their stability and properties. The high strength of the OPb4 te trahedral units involves interplay between high basicity of additional O2– anions and stereochemical activity of the 6s2 lone electron pairs on Pb2+ cations. The structural chemistry of polycations based upon OPb4 tetrahedra, in general, follows major trends previously observed for cation-centered tetrahedral units (silicates, phosphates, metal sulphides with MS4 tetrahedra, etc.). One may conclude that the basic structural correlations depend upon size and charge parameters of the ions only, irrespective of their positive or negative sign.

Algorithm for Calculating the Thermal Expansion Tensor and Constructing the Thermal Expansion Diagram for Crystals

A new program package based on the Microsoft Windows operational systems is proposed for thermal investigations of crystals. The package consists of two programs, one of which provides a means for calculating the thermal expansion tensor for crystals of any symmetry and the second program is intended for drawing three-dimensional thermal expansion diagrams. The calculation and drawing procedures are described.

Software for determining the thermal expansion tensor and the graphic representation of its characteristic surface (theta to tensor-TTT)

A software is developed for determining the parameters of the thermal expansion tensor of the crystals of any system by a set of experimental diffraction data received using X-ray, synchrotron and other radiations at various temperatures. An algorithm is realized which allows carrying out all calculations from the experimental determination of the Bragg reflection angles to the calculation of the parameters of the thermal expansion tensor of the crystals, including the orientation of the tensor axes with respect to the crystallographic axes. The drawing of the 3D characteristic surface of the tensor and its 2D sections is also provided. The software is aimed at studying the anisotropy of the thermal expansion of the crystal materials and phase transitions, as well as revealing the mechanism and nature of the thermal behavior of substances.

High-temperature borate crystal chemistry

Abstract The paper presents a brief review of the present state of high-temperature borate crystal chemistry. This review summarizes the results of high- and low-temperature single crystal X-ray diffraction studies for more than 10 borate structures and high-temperature powder Xray diffraction data for about 65 borates. Thermal behavior of their crystal structures, thermal expansion, polymorphic transitions and their relationship to borate glasses are presented. These studies allow to formulate the basic principles of high-temperature borate crystal chemistry and to reveal the regularities of thermal behavior of borates. On heating, the BO3 and BO4 polyhedra and rigid groups consisting of these polyhedra, practically maintain their configuration and size, but they are able to rotate like hinges exhibiting highly anisotropic thermal expansion, including linear negative expansion. Based on these results, we generalize the term “rigid group” and render thermal vibrations as the key ingredient for the self-assembly of borate rigid groups.

Phase transitions of n-alkanes as rotator crystals

Abstract Phase transitions of n -alkane homologues with n =17–24, their solid solutions, two-phase mixtures and multicomponent mixtures with n =17–37, of biological, geological and technological origin have been studied by high-temperature X-ray powder diffraction. In keeping with the rotator nature of n -alkanes, their thermal deformations and polymorphic transformations are discussed as a function of the thermal torsional motion of the molecules. We have shown that not only orthorhombic n -alkanes but also triclinic n -alkanes undergo consistent phase transitions from the crystal state (cryst) to the low-temperature (rot.1) and high-temperature (rot.2) rotator states. When molecules (atoms) of different kinds combine in a structure one more rotator state of n -alkanes (rot.1+2), intermediate between the low-temperature (rot.1) and high-temperature (rot.2) rotator states, was identified. Each of these states is characterized by a specific form of the molecular thermal oscillation motion. The existence of crystal phase V and rotator phase RV is discussed on the basis of X-ray powder diffraction and literature data. Phase transitions of the mixtures of two crystal phases were shown to depend on the molecular symmetry (parity) of the mixed components and the difference in chain length (Δ n ). The distinguishing feature of the phase transition to the rotator state of multicomponent mixtures is step-wise phase separation of the solid solution during heating.

New layered polyanion in α-CsB5O8 high-temperature modification

Crystal structure of high-temperature polymorphic modification, α-CsB5O8, was determined from single-crystal X-ray diffraction data. The phase crystallizes in space group P21/c with a = 7.122(2), b = 9.640(3), c = 11.411(3) A, β = 116.64(2) ◦ and V = 700.3(3) A 3 , Z = 4. It contains new zigzag layer polyanions built up from rigid [B5O8] − pentaborate groups that consist of four triangles and a tetrahedron condensed to a double ring via common tetrahedron. The cesium cations are located in large cavities of the layers and they are coordinated by nine oxygen atoms with distances from 3.037 to 3.429 A. Five of the oxygen atoms are placed in the same layer as cesium atom; other four ones are distributed between two adjacent layers. Under heating this structure demonstrates a highly anisotropic thermal expansion (α11 = 27, α22 = 61, α33 =− 8 × 10 −6 K −1 ); the thermal expansion in the direction perpendicular to the layer is the intermediate one.  2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.

Prewittite, KPb1.5Cu6Zn(SeO3)2O2Cl10, a new mineral from Tolbachik fumaroles, Kamchatka peninsula, Russia: Description and crystal structure

Abstract Prewittite, ideally KPb1.5Cu6Zn(SeO3)2O2Cl10, was found in the fumarole field of the second cinder cone of the North Breach of the Great fissure Tolbachik eruption (1975-1976, Kamchatka peninsula, Russia). It occurs as separate olive-green tabular crystals up to 0.2 mm in maximum dimension. It has vitreous luster and brownish-green streak. Prewittite is orthorhombic, space group Pnnm, a = 9.132(2), b = 19.415(4), c = 13.213(3) Å, V = 2342.6(9) Å3, Z = 4, Dcalc = 3.89 g/cm3, Dmeas = 3.90(2) g/cm3. The eight strongest lines of the powder X-ray diffraction pattern are {I [d(Å)] hkl}: 70 (8.26) 110; 60 (7.53) 101; 90 (4.111) 220, 132, 141; 100 (3.660) 212, 123; 40 (2.996) 223; 50 (2.887) 062; 40 (2.642) 322, 214; 40 (2.336) 073, 180, 244. Prewittite is biaxial (-). The optical orientation is X = a, Y = c, Z = b. The mineral has clear pleochroism: X, Y - olive green, Z - red-brown. The mineral is very brittle with the perfect cleavage on (010) and (101). The most developed crystal forms are {010}, {001}, and {101}. The chemical composition determined by the electron-microprobe is (wt%): K2O 1.76, PbO 21.18, CuO 33.24, ZnO 8.00, SeO2 15.74, Cl 26.06, O=Cl -5.88, total 100.10. The empirical formula derived on the basis of O+Cl = 18 and sum of positive charges of cations equal to 26 is K0.53Pb1.33Cu5.87Zn1.38Se1.99O7.67Cl10.33. The crystal structure was solved by direct methods and refined to an agreement index R1 = 0.034 on the basis of 1522 independent reflections with I ≥ 2σI. It is based upon metal oxide selenite chloride layers parallel to (010) and linked through K-Cl and Pb-Cl bonds to the K and Pb atoms located in the interlayer. The mineral name honors Charles T. Prewitt (b. 1933) in recognition of his important contributions to crystal chemistry of minerals and planetary materials.

XRD and DSC study of the formation and the melting of a new zeolite like borosilicate CsBSi5O12 and (Cs,Rb)BSi5O12 solid solutions

Polycrystalline CsBSi5O12 was prepared from a stoichiometric mixture by solid-state reaction above 1000 °C. The solid solutions Cs1–xRbxBSi5O12 were obtained at 1000 °C during a long heat treatment of polycrystalline Cs1–xRbxBSi2O6 boropollucites (xRb = 0, 0.05, 0.2, 0.4). A new borosilicate compound and its solid solutions were studied using X-ray powder diffraction (XRD), annealing, differential scanning calorimetry (DSC), and thermogravimetry (TG). For Cs,Rb-boropollucites the new phase formation is accompanied by significant mass losses detected by DSC and TG. The following mechanism of phase transformations is assumed: (Cs,Rb)BSi2O6 → (Cs,Rb)BSi5O12 + (Cs,Rb)BO2↑. The zeolite phase forms as a result of the boropollucite decomposition over 1000 °C. Zeolite decomposes also on further heating and the SiO2 reflections are observed in the XRD pattern only. Thus above 1000 °C both boropollucite and zeolite phases are unstable presumably due to the ability of the alkali cations to leave the structure. Using XRD the unit cell parameters of CsBSi5O12 have been determined in the orthorhombic crystal system: a = 16.242(4) Å, b = 13.360(4) Å, c = 4.874(1) Å. The compound is isostructural with the zeolite compound CsAlSi5O12. In the crystal structure of Cs1–xRbxBSi5O12 solid solutions the changes of cell parameters are insignificant under the substitution of Cs by Rb atoms that indicates a very limited substitution range.

The crystal structure of averievite, Cu 5 O 2 (VO 4 ) 2 .nMX; comparison with related compounds

Abstract The crystal structure of averievite, Cu5O2(VO4)2‧nMX has been determined. Trigonal system, space group P3, a = 6.375(1), c = 8.399(1) Å, V = 295.6(1) Å3, Z = 1, Dx = 4.01(1) g/cm3. The atomic arrangement is characterized by infinite nets parallel to (001) composed of [OCu4]6+ tetrahedra linked via corners in hexagonal rings. The bases of neigbouring tetrahedra are in one plane and their non-shared corners are turned to the oppoosite sides. The [VO4]3- tetrahedra are attached to the bases of [OCu4] tetrahedra. There are large (R >3.2 Å) channels in the structure where large molecular particles can enter. The comparison of the averievite structure with related compounds (in particular, copper oxovanadates) is given from the point of view of [OT4] polyion crystal chemistry.