Vadim M. Kovrugin

Dimers of oxocentred [OCu4]6+ tetrahedra in two novel copper selenite chlorides, K[Cu3O](SeO3)2Cl and Na2[Cu7O2](SeO3)4Cl4, and related minerals and inorganic compounds

Abstract Two novel copper selenite chlorides, K[Cu3O](SeO3)2Cl (I) and Na2[Cu7O2](SeO3)4Cl4 (II), have been synthesized by the CVT method. Their crystal structures have been solved by direct methods and refined by least-squares techniques. I is triclinic, space group P1̅, a = 7.6821(5), b = 8.1179(5), c = 8.7836(6) Å, α = 113.193(3), β = 108.735(4), γ = 98.245(4)°, V = 453.32(5) Å3, R1 = 0.0481 for 1210 unique reflections with F ≥ 4σ(F); II is triclinic, space group P1̅, a = 7.4362(6), b = 8.3361(7), c = 9.1343(11) Å, α = 110.277(6), β = 106.212(6), γ = 105.158(4)°, V = 467.94(8) Å3, R1 = 0.0265 for 2498 unique reflections with F ≥ 4σ(F). The structures of I and II can be described in terms of dimers of copper oxocentred tetrahedra. In I, two (OCu4)6+ tetrahedra share a common Cu···Cu edge to form the [O2Cu6]8+ dimer, whereas the structure of II is based upon two (OCu4)6+ tetrahedra linked together by one common Cu atom resulting in the formation of the [O2Cu7]10+ dimer. A comparison with related minerals and inorganic compounds is given.

pH controlled pathway and systematic hydrothermal phase diagram for elaboration of synthetic lead nickel selenites.

The PbO-NiO-SeO2 ternary system was fully studied using constant hydrothermal conditions at 473 K. It yields the establishment of the corresponding phase diagram using a systematic assignment of reaction products by both powder and single-crystal X-ray diffraction. It leads to the preparation of three novel lead nickel selenites, α-PbNi(SeO3)2 (I), β-PbNi(SeO3)2 (II), and PbNi2(SeO2OH)2(SeO3)2 (III), and one novel lead cobalt selenite, α-PbCo(SeO3)2 (IV), which have been structurally characterized. The crystal structures of the α-forms I, IV, and III are based on a 3D complex nickel selenite frameworks, whereas the β-PbNi(SeO3)2 modification (II) consists of nickel selenite sheets stacked in a noncentrosymmetric structure, second-harmonic generation active. The pH value of the starting solution was shown to play an essential role in the reactive processes. Magnetic measurements of I, III, and IV are discussed.

[NaCl][Cu(HSeO3)2], NaCl-intercalated Cu(HSeO3)2: synthesis, crystal structure and comparison with related compounds

Abstract Single crystals of [NaCl][Cu(HSeO3)2] have been prepared by the chemical vapor transport reactions. Its crystal structure (monoclinic, C2/c, a = 13.9874(7), b = 7.2594(4), c = 9.0421(5) Å, β = 127.046(2)°, V = 732.81(7) Å3) is based upon electroneutral [Cu(HSeO3)2] sheets formed by corner sharing between the [CuO4] squares and (HSeO3) groups that are parallel to the (100) plane. Each (SeO2OH)– group forms the Oh1...O2 hydrogen bond to an adjacent hydroselenite group to constitute a [(SeO2OH)2]2– dimer that provides additional stabilization of the copper diselenite sheet. The [Cu(HSeO3)2] sheets alternate with the sheets consisting of zigzag–Na–Cl–Na–Cl–chains formed by Cl atoms and disordered Na sites. The chains are parallel to the c axis. The linkage between the alternating electroneutral [Cu(HSeO3)2] and [NaCl] sheets is provided by the Cu–Cl and Na–O bonds. The coordination of Na is fivefold and consists of three O and two Cl atoms. [NaCl][Cu(HSeO3)2] is a new member of the group of compounds based upon the M(HSeO3)2 layers (M2+ = Cu, Co, Cd). The prototype structure for this group is [Cu(HSeO3)2] that does not have any chemical species separating the copper hydroselenite layers. In other compounds, the interlayer space between the [Cu(HSeO3)2]0 layers is occupied by structural units of different complexity. [NaCl][Cu(HSeO3)2] can be considered as [Cu(HSeO3)2] intercalated with the NaCl layers consisting of one-dimensional–Na–Cl–Na–Cl–chains.

Structural variety of novel Pb and Bi selenites

Selenium-containing lead and bismuth compounds are of special interest since of their geochemical and mineralogical abundance. During the last decade there has been a surge of research activity in the study of PbO/Bi2O3– MxOy–SeO2 (M = Cu 2+, Ni2+, Fe3+, V5+; x=1,2; y=1,3,5) ternary system. The asymmetric [SeO3] 2– selenite groups with stereochemically active s2 lone electron pair, and Pb2+/Bi3+ cations with highly irregular coordination increase the chance to achieve non-centrosymmetric crystal structures. This may give rise to the discovery of novel polar materials with various applications. Here, we report on the synthesis, characterization, and structure of eight novel lead and bismuth selenites containing different transition metals. The crystals of three novel lead selenites with nickel α–PbNi(SeO3)2 (I), β–PbNi(SeO3)2 (II), and PbNi2(SeO3)2(SeO2OH)2 (III), and two lead vanadate selenites Pb4(V3O8)2(SeO3)3 (IV), and Pb2(VO2)(SeO3)2Cl (V) were obtained by hydrothermal method from aqueous solutions of PbO, SeO2, and NiO (for I–III) or V2O5 (IV, V). The compound Mn2(Bi2O)(SeO3)4 (VI) was prepared in a similar manner from aqueous solution of SeO2, BiOCl, Mn2O3, and MnO2. The reactions were performed in 23 mL Teflon-lined Parr reaction vessels heated in Thermo Scientific mechanical convection oven up to 200°C (I, V, VI), 220°C (II), 180°C (III), 210°C (IV). The products of novel selenites consisted of greenishyellow platy crystals of I–III and reddish-brown prismatic crystals of IV–VI up to 300 μm in maximal dimension. The crystals of two novel bismuth selenites Bi6(SeO3)4Cl10 (VII), and MnBi(SeO3)2Cl (VIII) were prepared by the solid-state reaction method. The mixture of Bi2O3, BiCl3, SeO2, and Mn2O3 powders was pressed into a disk, which was subsequently sealed in an evacuated silica-glass tube and heated at 400°C. The products consisted of transparent (VII) and brown platy crystals (VIII) ranging in maximal dimension up to 400 μm. Crystals selected for data collection were mounted on a Bruker DUO four-circle diffractometer equipped with an APEX II CCD detector and monochromated MoKα radiation. The structures were solved by direct methods. Traditional inorganic crystal chemistry based upon the concept of cation-centered polyhedra is applied to the most of the selenites reported herein. However, the structure of VI is described as consisting of strongly bonded structural units formed by oxocentered coordination polyhedra. Structural investigations revealed that the structures under consideration are based upon structural units of various shape and dimensionality.

Synthesis and structural variety of first Mn and Bi selenites and selenite chlorides

Abstract Single crystals of new Mn2[Bi2O](SeO3)4 (I), MnBi(SeO3)2Cl (II), MnIIMnIII(SeO3)2Cl (III), Mn5(SeO3)2Cl6 (IV), and Mn4(Mn5,Bi)(SeO3)8Cl5 (V) have been synthesized by chemical vapour transport and hydrothermal methods. They have been structurally characterized by single crystal X-ray diffraction analysis. The compounds II–V are the first Mn selenite chlorides, while the I, II and V compounds are the first Bi-containing Mn oxoselenites. Structural relationships of the new phases with other compounds are discussed. An overview of the mixed-ligand MnOmCln polyhedra in inorganic compounds is given.

Modular crystallography of novel copper selenites and selenates: experimental mineralogy

Selenium oxysalts (selenites [4+] and selenates [6+]) occur relatively rare in natural environments even in comparison with, e.g., anoxic selenides [2–]. At the same time, Se-containing oxycompounds adopt a wide variety of atomic arrangements and crystal structures. For example, the interplay between stereochemical activity of lone electron pairs of Se4+ cations and the Jahn-Teller effect of spontaneous symmetry breaking in solids for a d9 electronic configuration of Cu2+ cations results in a number of crystal structures with unique structural topology. In particular, many natural and synthetic copper selenites have been shown to contain so-called ‘additional’ oxygen atoms, which are coordinated solely by Cu2+ cations resulting in the formation of oxocentered (OCu4)6+ tetrahedra combined into structural modules of different dimensionalities [1]. Herein, we present the results of our studies of a wide range of synthetic copper selenites and selenates, which have been prepared by different synthesis methods [2, 3]: chemical vapor transport reactions, evaporation from aqueous solutions, and mild hydrothermal techniques. These experiments can be considered as modelling of natural processes that occur in volcanic fumaroles or oxidation zones of copper mineral deposits. Topological relationships of the observed compounds with crystal structures of existing mineral species will be discussed. This work was supported by the Russian Science Foundation (grant 14-17-00071) and the St. Petersburg State University provided financial support for participation in the XXIV Congress of the IUCr 2017.