N. V. Pervukhina

Crystal Chemistry of Dichalcogenides MX2

Crystal-chemical analysis of the structures of metal (other than REE) dichalcogenides of composition X:M = 2:1 has been carried out. It is shown that there are two types of structure depending on the formal degree of metal oxidation. The first group are compounds M(X2) containing metals in the oxidation state 2+ and covalently bonded pairs of chalcogen elements; the main structural types here are cubic (pyrite) and orthorhombic (marcasite) FeS2. The second group involves the compounds MX2 with metals in the formal oxidation state 4+ and chalcogenide ions X2-; the main structural types in this group are CdI2, CdCl2, MoS2. The bond lengths M–X, X–X, and X...X are analyzed; it is shown that the high polarizability of the chalcogenide ions is reflected in shortened X...X distances. In the covalently bonded pairs X–X, the bond lengths change within the following limits: 2.03-2.30, 2.35-2.55, and 2.70-2.83 Å for X...X ion contacts, the minimal values are 3.07, 3.10, and 3.20 Å (X = S, Se, and Te, respectively).

Analysis of atomic structures as the development of Belov’s “lattice” crystallography

The theorems of lattice crystallography, which was developed by N.V. Belov, and the wave-mechanical concept of the crystalline state lie in the basis of the crystallographic analysis of structures, which determines the results of atomic ordering by sets of crystallographic planes with the formation of pseudotranslational sublattices (force skeletons of structures). The role of cationic and anionic sublattices is shown by the example of structures of natural sulfides: heyrovskyite Pb6Bi2S9 and cannizzarite (Pb,Cd)5(Bi,In)6(S,Se)14.

Crystallographic analysis of a series of inorganic compounds

The method of crystallographic analysis relies on the mechanical-wave concept that treats the crystalline state as the result of ordering of atomic positions by families of parallel equidistant planes. Using this method, a large set of fluoride, oxide and sulfide structures was analyzed. The pseudo-translational ordering of various atomic groups (including the presence of cation and anion sublattices) in the structures of various classes of inorganic compounds was established. The crucial role of local ordering of heavy cations (coherent assembly) in the structures comprising large cluster fragments (Keggin polyanions, polyoxoniobates, etc.) is discussed. The role of symmetry and the regular distribution of heavy atoms in the formation of stable crystal structures, which is to be taken into account in the targeted design, is considered. The universality of configurations of atomic positions in the structures of various classes of inorganic compounds resulting from the ordering mechanism organized by mechanical (elastic) forces is demonstrated. The bibliography includes 158 references.

Crystal chemistry of mercury(I) and mercury(I, II) minerals

The crystal structures of 16 mercury(I)- and mercury(I, II)-containing minerals having (Hg-Hg)2+ groups are considered. The Hg-Hg and Hg-X bond lengths and the HgHgX angles (X = Cl, Br, I, O, S) are analyzed. A comparative crystal chemical analysis of the environment of Hg atoms is carried out. The Hg-Hg and Hg-X distances vary within 2.43-2.60 and 1.93-2.43 å, respectively; the angles defining the deviation of the X-Hg-Hg-X groups from linearity are from 146 to 177‡. In most cases, the coordination environment of the mercury atoms involves the metal atom of the (Hg-Hg)2+ dumbbell and the X atom, but in several compounds the coordination number of the mercury atoms increases due to the additional atoms lying 2.5–3.5 å away. In terlinguaite and kuznetsovite, the Hg3 triangle is rather unusual; in the latter mineral, the Hg-Hg bonds are lengthened to 2.64-2.70 å. The review covers structural data up to May 1997.

Experimental Crystallography from Atomic to Supramolecular Scale

Results of crystal structure analysis for various types of compounds are discussed in terms of a new concept of crystal formation. The effect of ordering “rigid” atomic groups ([Hg2]2+, [H2As · W18O60]7-, etc.) by families of crystallographic planes with interplanar distances comparable to the sizes of the groups is considered. The wide occurrence of symmetrical packings of atoms and/or centers of rigid atomic groups in structures is explained by a tendency toward maximum reduction in the number of degrees of freedom and, hence, a tendency toward minimum energy of the system.

Oxocentered polycationic complexes — An alternative approach to crystal-chemical investigation of the structure of natural and synthetic mercury oxosalts

The crystal structures of mercury oxosalts are described with isolation of oxocentered tetrahedrul groups [OHg4]. The bond topology of the oxocentered polycations is more diversified and rich than the motifs of canonic polyhedra in “classical” crystal chemistry and often is a more striking illustration of the unique nature of the structure of compounds from this class. The relative stability of the oxocentered polyions indicates that they play an important role in structure formation and possibly exist in various natuml media, making it appropriate to consider these groups in analysis of mercury transfer processes occurring in nature. The oxocentered approach proved to be useful for establishing structure-property type correlations and promotes the understanding and predicting the anisotropy of physical properties.

Coherence assembly phenomenon in the typical structures of heteropolyniobates

Crystallographic analysis has provided evidence for single cation frameworks formed from preordered cation positions in the individual building blocks (modules) constituting the basis of structures. We propose to call this phenomenon coherence assembly. According to the mechanical wave concept of the crystalline state, coherence assembly dictates the rules of mutual packing of “rigid” structural fragments. This study investigates the typical structures of heteropolyniobates: Na12[Ti2O2][SiNb12O40]·4H2O (I), menezesite Ba2MgZr4[BaNb12O42]·12H2O (II), and the menezesite-isostructural aspedamite □12(Fe3+,Fe2+)3Nb4·[Th(Nb,Fe3+)12O42]·(H2O,OH)12 (III).

Structure and properties of terbium(III) dipivaloylmethanate and its adducts with Bipy and Phen

The complex of terbium(III) with dipivaloylmethane (2,2,6,6-tetramethylheptane-3,5-dione = Htmhd) [Tb(tmhd)3]2 (1) and two its adducts with bipyridyl (Bipy) and phenanthroline (Tb(tmhd)3·Bipy (2) and Tb(tmhd)3·Phen (3)) are synthesized and analyzed by single crystal X-ray diffraction. The crystals of [Tb(tmhd)3]2 (1) belong to the monoclinic crystal system: P21/n space group, a = 12.2238(2) Å, b = 27.6369(5) Å, c = 21.8740(4) Å, β = 105.146(1)°, V = 7133.0(2)Å3, Z = 4; the crystals of Tb(tmhd)3·Bipy (2) and Tb(tmhd)3·Phen (3) belong to the triclinic crystal system with unit cell parameters: (2)

Structure of dysprosium polysulfide DyS1.83 (Dy6S11) according to x-ray diffraction analysis

P\bar 1

Crystallographic analysis of microtwin structures of sulfides: The case study of lillianite and heyrovskyite

space group, a = 11.0554(6) Å, b = 12.2761(7) Å, c = 17.7096(8) Å, α = 77.457(2)°, β = 85.557(2)°, γ = 69.659(2)°, V = 2199.8(2) Å3, Z = 2; (3)