Simulation of self-organization processes in crystal-forming systems: Supramolecular cyclic R6 cluster precursors and self-assembly of TeO2-TEL (Tellurite) and TeO2-PAR (Paratellurite) structures

The supramolecular chemistry of oxides of sp elements (SO₂, SeO₂, and TeO₂) is considered. The self-assembly of TeO₂-TEL (Tellurite) and TeO₂-PAR (Paratellurite) crystal structures is simulated. Methods of combinatorial and topological analysis (TOPOS program package) are applied which are based on constructing a basis 3D network of the structure in the form of a graph, the sites of which correspond to the positions of centroids of TeO₂ molecules and the edges characterize bonds between them. The topological type of the basis 2D network in the TeO₂-TEL structure corresponds to graphite (C-GRA), while in the TeO₂-PAR structure the basis network corresponds to the 3D diamond network (C-DIA). A nanocluster precursor of cyclic type (R6) composed of six covalently bound TeO₂ molecules (chair conformation) is established for both structures. The desymmetrization of the cyclic structure of the R6 cluster in TeO₂-PAR is related to the formation of Te-Te bonds with lengths of 3.824 and 4.062 Å. The symmetry and topology code of the processes of self-assembly of 3D structures from nanocluster precursors is completely reconstructed into the form “primary chain → microlayer → microframework.” In both structures R6 clusters form 2D packings with a coordination number of 6. The cluster self-assembly model explains the specific features of the morphogenesis of TeO₂-TEL and TeO₂-PAR (phases with low and high crystallization temperatures, respectively): platelike shape, perfect cleavage in the (110) plane, and preferred growth in the primar-chain direction [100] in the former case and growth in the direction of the primary [001] axis with the preferred formation of tetragonal prism faces (110) in the latter case.     

Influence of the Mechanism of the Initial Stages of the Ligand Decomposition on the Initiating Ability of Cobalt(III) Ammine Tetrazolate Complexes

Russian Journal of General Chemistry - The results of quantum chemical calculations for isolated molecules of pentaammine-(5-cyano-2H-tetrazolato-N2)cobalt(III) perchlorate,...     

Cluster self-organization theory for crystal-forming systems: The geometrical and topological model of formation, selection, and evolution of precursor nanoclusters of molecular and framework compounds

This review concerns the contemporary state of the problem of self-organization in crystal-forming systems, where a long-range order appears spontaneously in the arrangement of nanoscale structural units of any nature (atomic clusters and molecules), which initially existed as a chaotic mixture. Examples are provided where combinatorial topological analysis algorithms are used to restore, from structure data, the convergent matrix self-assembly code of crystal structures in the form of the sequence of significant elementary events e _i . For a cyclic six-node cluster S ₃ ⁰ , the geometrical and topological modeling of various self-organization levels of hierarchic structures was carried out for six types of primary chains S ₃ ¹ , fifteen types of networks S ₃ ² , and thirty types of frameworks S ₃ ³ . The model is universal and has been used to model the self-assembly of the following crystal structures: monomolecular compound S₆ and bimolecular compound S₆ + S₁₀, ozone O₃, benzene C₆H₆, cubane C₈H₈, Zn₄O₄ (NaCl structure type), carbon oxides C₆-GRA (graphite), C₆-DIA (diamond), and C₆-LON (lonsdaleite), boron nitrides B₃N₃-GRB, B₃N₃-DIA, and B₃N₃-LON, Ni₃As₃-NIC, B₆(OH)₁₆, zeolite K₃(Al₂Si₄O₁₂(OH)-LIT, Na₂ZrSi₂O₇-PKL (parakeldyshite), La₃Ga₅GeO₁₄ (LGG), and La₃GaGe₅O₁₆ (LAN). It is for the first time that structural invariants are recognized in topologically different crystal structures of chemical systems. Bifurcations in the evolution pathways of precursor clusters (structural branching points) have been determined for the formation of three-dimensional periodic structures. Frequency analysis carried out for the topological and symmetry pathways in the formation and evolution of clusters (primary chain S ₃ ¹ -microlayer S ₃ ² -microframework S ₃ ³ ) elucidated new crystal-formation trends in diverse chemical systems at the microscopic level.     

Cluster Self-Organization of Intermetallic Systems: 124-Atom Cluster 0@12@32@80 and 44-Atom Cluster 0@12@32 for the Self-Assembly of Li48Na80Ga332-oF920 Crystal Structure

Crystallography Reports - A combinatorial and topological analysis has been performed and self-assembly of the Li48Na80Ga332-oF920 crystal structure has been simulated (sp. gr. Fmmm, a = 24.666...     

Cluster self-organization of silicate and germanate systems: Suprapolyhedral precursor nanoclusters and self-assembly of tetrahedral structures of the family A2T2O5 (A = Li, Na; T = Si, Ge): Li2T2O5, Li4Ge3SiO10, Li2Si2O5, and A2Si2O5

Modeling of atomic species (An clusters in the form of atoms or Kn polyhedra, where n is the number of atoms or polyhedra) corresponding to the initial stage of evolution of a chemical system has been carried out. Three series of K4 clusters built of different T tetrahedra (L and T) have been recognized. For L₂T₂ clusters, six geometrically and symmetrically different types of suprapolyhedral clusters have been discovered. The model has been used to identify precursor clusters in A₂T₂O₅ (A = Li, Na; T = Si, Ge) framework structures: A-type Li₂T₂O₅ with space group Cc, B-type Li₄Ge₃SiO₁₀ with space group Abm2, C-type Li₂Si₂O₅ with space group Ccc2, and D-type A₂Si₂O₅ with space group Pbcn. Three (of the six possible) types of suprapolyhedral precursor nanoclusters K4 in the four structures have been identified. The full 3D reconstruction of the self-assembly scenario of crystal structures is as follows: precursor nanocluster ?? primary chain ?? microlayer ?? microframework ?? ?? framework. The bifurcation of structural evolution pathways (structural branching points) at the suprapolyhedral level for type A and B structures is found to occur only when a microframework is formed of equivalent microlayers.     

Cluster self-organization of Na-TR-Ge-O-H (TR = La-Lu, Y, and Sc) germanate systems: Suprapolyhedral precursor clusters and self-assembly of Na2Pr6Ge8O26, Na4Sc2Ge4O13, and Na5ScGe4O12 crystal structures

In an M-T-O model system (M is a polyvalent metal; T = Ge or Si), we consider initial stages of formation of cyclic MT clusters and the mechanism of their modification by T tetrahedra. The polyhedron ratio T/M in clusters increases progressively during modeling from one in M₂T₂ to two (M₂T₂ + 2T = M₂T₄), three (M₂T₂ + 2T₂ = M₂T₆), and four (M₂T₂ + 2T + 2T₂ = M₂T₈). These types of clusters were used to find precursor clusters for T-condensed structures of Na₂Pr₆Ge₈O₂₆, Na₄Sc₂Ge₄O₁₃, and Na₅ScGe₄O₁₂. The TOPOS program package was used to carry out the complete 3D reconstruction of the self-assembly of Na,TR germanates: precursor cluster → primary chain → microlayer → microframework (supraprecursor) → ... framework. In all structures, as previously in six orthotetrahedral Na,TR germanate structures, the basic invariant type of four-polyhedral cyclic precursor cluster M₂T₂ was identified; this cluster is built of TR polyhedra, with CN = 6 or 7, linked via orthotetrahedra. The features of the generation of a Ge radical were considered in the form of a Ge₂O₇ chain and a Ge₄O₁₂ ring in various layers of the Na₂Pr₆Ge₈O₂₆ composite structure, a Ge₄O₁₃ chain in Na₄Sc₂Ge₄O₁₃, and a Ge₁₂O₃₆ ring in the Na₅ScGe₄O₁₂ superionic conductor. Original Russian Text ? G.D. Ilyushin, L.N. Dem’yanets, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 3, pp. 484–496.     

Influence of the surface microroughness of a Si(001) substrate on the morphology of CaF2 epitaxial layers under high-temperature growth conditions

The influence of the surface microroughness of Si(001) substrates on the morphology of CaF₂ epitaxial layers is investigated in the high-temperature growth mode. The atomic-force microscopy method is used to demonstrate that the silicon surface relief substantially affects the nucleation, growth, and formation of the morphology of CaF₂ layers.     

The Effect of Ionizing Preirradiation of Energy-Saturated Materials on Their Susceptibility to Irradiation with a High-Current Electron Beam

The susceptibility of two types of energy-saturated materials (composition VS-2, which is an energy-saturated metal-inorganic compound with minor additions of a polymer binder, and an energy-saturated composite of NCP and fullerene) preirradiated with β particles and γ quanta to irradiation with a high-current nanosecond electron beam is studied. The obtained results demonstrate that the preirradiated energy-saturated materials are significantly more susceptible to electron irradiation. This effect lasts for at least eight months and is more pronounced in the case of gamma-preirradiation.     

Knockout of deuterons and tritons with large transverse momenta in <Emphasis Type="Italic">pA</Emphasis> collisions involving 50-GeV protons

Formation of the d and t cumulative light nuclear fragments emitted from the nucleus with large transverse momenta at an angle of 35° in the laboratory frame is investigated. The data on collisions of 50-GeV protons with the C, Al, Cu, and W nuclei are collected using the extracted proton beam of the IHEP accelerator and the SPIN detector. The results indicate that the dominant contribution to formation of nuclear fragments comes from the local process of direct knockout from the nucleus.     

Features of the surface morphology of CaF<Subscript>2</Subscript>/Si(100) films obtained by solid-phase epitaxy

The dielectric parameters of calcium fluoride films grown on the Si(100) surface by solid-phase epitaxy (group 2) and without it (group 1) are analyzed. It is established experimentally that the deposition mode of CaF₂ films immediately after growth of the Si buffer layer at a substrate temperature of 530°C is not suitable for producing high-quality dielectric layers. The use of solid-phase epitaxy at the initial stage of the nucleation of CaF₂ layers enables the production of single crystal uniformly thick films with high dielectric properties.