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The crystallographic analysis of the structures of Yb3(BO3(OH)6)·2H2O (I), Ba8Ni4[BP3O11(OH)2]4 (II), and Pb4(O(OH)2)SiO4 (III) shows that they are based on sublattices of heavy Yb, Ba, Pb cations with similar parameters and a significant fraction of vacant nodes, which provides the formation of bulk voids. The key role of these cations also manifests itself in the fact that they occupy special positions with fixed coordinates and a high local symmetry. The crystallization process is a coherent assembly of chemically stable cation groups formed in the precrystallization phase of a substance. [ABSTRACT FROM AUTHOR]

The model of the occurrence of translational symmetry as a complex of standing plane elastic waves, forming three-dimensional lattices of their intersection nodes, is proposed based on the results of a crystallographic analysis of popular structure types. Criteria of crystal structure stability, characterizing the reduction of atomic degrees of freedom, are proposed taking into account the additional symmetric atomic ordering in the unit-cell volume. The characteristics of some highly symmetrical structures with cubic or hexagonal symmetry are compared. It is proposed to refer to the process of formation of stable states by creating symmetric spatial configurations, which is universal for material particles, as crystal dynamics. [ABSTRACT FROM AUTHOR]

Results of the crystallographic analysis of monoclinic Lu5Ba6B9O27 = Lu5Ba6(BO3)9 (I) and orthorhombic Sr3Bi2(BO3)4 (II) orthoborate structures are discussed in terms of crystal dynamics (mechanical and energetic processes underlying the formation of translational and point symmetries). The templates in both cases are massive and crystallochemically active cations (Lu, Bi) localized, together with their anionic environments, at fixed symmetry-determined sites. The centers of BO3 groups are partially included in the sublattice of heavy cations, and their relative orientation complies with the local symmetry of the templates. [ABSTRACT FROM AUTHOR]

Based on the crystallographic results, the crystal structure formation mechanism (crystal dynamics) of KCaNd(BO3)2 and BaB2O4 compounds is presented. Close similarity of the first structure with aragonite CaCO3 and of the second with hexagonal carbonates is shown. High pseudo-symmetry is noted, bringing the structures to the maximum symmetry possible for hexagonal crystals. [ABSTRACT FROM AUTHOR]

The geometry of cation and anion matrices is analyzed in the crystal structures of complex sulfides with the symmetry mirror planes perpendicular to the short translation of ~4 Å. In support of the developed crystalline state concept, the structures exhibit the spatial atomic ordering by the systems of crystallographic planes. This includes the absolute ordering by the symmetry mirror planes that tend to form hexagonal sublattices with trigon 36 nets. [ABSTRACT FROM AUTHOR]

Tendencies in modern crystal chemistry, such as the representation of crystal structures in the form of planar atomic nets of different geometry and the simulation (assembly) of structures from “building blocks” of different complexity, have been briefly analyzed in terms of the original concept of the crystalline state. [ABSTRACT FROM AUTHOR]

Single crystals of two new mercury thiohalides of the composition Hg3S2Cl2− x Brx( x = 0.5) have been grown from gas phase and studied by X-ray crystallography. Structure refinement for monoclinic (I) and cubic (II) phases (I: a = 16.841(2) Å, b = 9.128(2) Å, c = 9.435(4) Å; β = 90.080(10)°, V = 1450.3(7) Å3, space group C2/m, Z = 8, R = 0.0528; II: a = 18.006(2) Å, V = 5837.8(11) Å3, space group $$Pm\bar 3n$$ , Z = 32, R = 0.0503) clearly shows that they are polymorphs of the same composition Hg3S2Cl1.5Br0.5. The monoclinic modification I is similar to the synthetic phases γ-Hg3S2Cl2, β-Hg3S2Br2, Hg3Se2Br2 and to the analogue of radtkeite mineral, Hg3S2ClI. The modification II is isostructural to the synthetic β-Hg3S2Cl2. In both structures, each S atom coordinates three Hg atoms with the formation of pyramidal SHg3 units (Hg-S 2.37–2.48 Å; HgSHg 93.1–97.5 ). The SHg3 units are linked through Hg vertices into corrugated layers [Hg12S8]∞∞ (I) and isolated cubic groups [Hg12S8] (II). Similarly to other mercury chalcohalides, the crystal structures are basically determined by the halogen atoms which form a cubic sublattice incorporating the Hg-S moieties. [ABSTRACT FROM AUTHOR]

The results of structural studies of the synthetic analog of the radtkeite mineral Hg3S2Cl1.00I1.00 are analyzed. The crystal structure of the compound has been refined; the unit cell parameters aream = 16.827(4) Å,bm = 9.117(1) Å,cm = 13.165(5) Å, ß = 130.17(2)°,V= 1543.3(8) Å3, space groupC2/m,Z= 8,R= 0.0527. A possible transitiona=am;b=am + 2cm;c= -bm to the pseudo-orthorhombicFcell previously determined for radtkeite, where one of the angles (?) is slightly different from 90° (89.55°), has been found. Each sulfur atom in the structure is bonded to three mercury atoms, forming SHg3 umbrellas with distances 2.240(6) Å-2.474(8) Å and angles HgSHg 94.7(2)°-102.9(2)°. The SHg3 fragments are linked through Hg vertices to form corrugated [Hg12S8]88 layers. The halogen atoms lie inside and between the [Hg12S8]88 layers; the distances are Hg-Cl and Hg-I 2.783(7) Å, 2.961(7) Å, and 3.083(4) Å-3.311(3) Å, respectively. [ABSTRACT FROM AUTHOR]

The results of structural studies of the synthetic analog of the radtkeite mineral Hg3S2Cl1.00I1.00 are analyzed. The crystal structure of the compound has been refined; the unit cell parameters aream = 16.827(4) Å,bm = 9.117(1) Å,cm = 13.165(5) Å, ß = 130.17(2)°,V= 1543.3(8) Å3, space groupC2/m,Z= 8,R= 0.0527. A possible transitiona=am;b=am + 2cm;c= -bm to the pseudo-orthorhombicFcell previously determined for radtkeite, where one of the angles (?) is slightly different from 90° (89.55°), has been found. Each sulfur atom in the structure is bonded to three mercury atoms, forming SHg3 umbrellas with distances 2.240(6) Å-2.474(8) Å and angles HgSHg 94.7(2)°-102.9(2)°. The SHg3 fragments are linked through Hg vertices to form corrugated [Hg12S8]88 layers. The halogen atoms lie inside and between the [Hg12S8]88 layers; the distances are Hg-Cl and Hg-I 2.783(7) Å, 2.961(7) Å, and 3.083(4) Å-3.311(3) Å, respectively. [ABSTRACT FROM AUTHOR]

The crystal-chemical structure of the minerals and inorganic compounds kuznetsovite [Hg3](AsO4)Cl and terlinguaite [Hg3][HgO2]Cl2, as well as [Hg3]3(AsO4)4 and [Hg3]2[HgO2](PO2 and their analogs, is considered from the viewpoint of the packing of large supramolecular atomic groups. The “cationic” layer of polyhedra around the large [Hg3]4+ cations, alternating with the anionic layer of [HgO2$]^\{2-\}$, (AsO4$)^\{3-\}$, (PO4$)^\{3-\}$, $\{\backslash rm\; Cl\}^-$, plays the major role in structure formation. Segregation of mercury cations of different valences possibly reflects the solid-state transformations occurring in nature and accompanied by mercury liberation. [ABSTRACT FROM AUTHOR]

On the basis of an original interpretation of the crystal state, it is shown that most of the structural types are determined by a small set of planar nets densely filled with the heaviest atoms of the structure. These nets are combined into atomic sublattices (matrices of the structure types) by the operations of (pseudo)symmetry, thus reducing the number of the degrees of freedom in the structure, which, in turn, provides structure stability. It is shown on examples of heavy-cation oxides, fluorides, and sulfides that the number of the types of such matrices (F-, I-, etc.) is limited. Each type is characterized by a certain structure-determining complex of mutually intersecting crystallographic planes parallel to the most densely filled atomic nets. Most of the atomic nets considered in crystal chemistry are, in fact, various sections of the sublattices-matrices formed by a limited number of densely filled atomic nets. [ABSTRACT FROM AUTHOR]