Cluster self-organization of germanate systems: Suprapolyhedral precursor nanoclusters and self-assembly of CAN-Na8(Al6Ge6O24)Ge(OH)6(H2O)2 and CAN-Cs2Na6(Al6Ge6O24)Ge(OH)6) zeolite crystal structures re]20100419

Geometrical and topological analysis of zeolite crystal structures having a tetrahedral framework of the cancrinite (CAN) type, namely, (CAN) Na₈(Al₆Ge₆O₂₄)Ge(OH)₆(H₂O)₂ (acentric space group P6₃, hP64, Na-CAN) and Cs₂Na₆(Al₆Ge₆O₂₄)Ge(OH)₆ (P6₃, hP52, CsNa-CAN), is carried out with the use of computer techniques (the TOPOS 4.0 program package). An AT ₆ hexapolyhedral precursor nanocluster centered with a template cation A (Na, Cs) is identified. The topological type of a two-dimensional (2D) crystalforming T-net 4.6.12, which corresponds to a uninodal semiregular Shubnikov net, is recognized. The full 3D reconstruction of crystal structure self-assembly is performed as follows: precursor nanocluster → primary chain → microlayer → microframework → … framework. The symmetry of an AT6 precursor nanocluster is described by point group 3; the symmetry axis passes through the center of the nanocluster and cation A. The coordination number (CN) of a precursor nanocluster, which characterizes the nanocluster stacking in the macrostructure, is six. In both structures, six Na atoms and a Ge(OH)₆ polyhedral species are spacers filling the voids between AT ₆ precursor nanoclusters. The Ge(OH)₆ polyhedral species is characterized by four and two orientationally allowed positions in Na-CAN and CsNa-CAN, respectively. The minimal number of suprapolyhedral AT ₆ precursor nanoclusters required for the 3D microframework to form is 16; that is, 96 tetrahedra are involved in microframework self-assembly.     

Mechanism of structural phase transitions in the Li4GeO4-ZnGeO4 system: Computer modeling and identification of invariant nanocluster structures in Li4GeO4, LISICON Li6Zn(GeO4)2, and Li4Zn2(GeO4)2 (γ phase)

The cluster modeling of structural phase transitions Li₄GeO₄ ?? LISICON Li₆Zn(GeO₄)₂ ?? ??-Li₄Zn₂(GeO₄)₂ was carried out using computer-assisted methods (the TOPOS program package). The precursor nanoclusters of crystal structures were recognized in an automated data processing mode using an algorithm developed for selecting combinations from nonintersecting suprapolyhedral clusters. 3D macro-structure modeling employed the principle of maximal space filling and, accordingly, took into account the requirement for the maximal complementary connectivity of precursor nanoclusters in crystal structure self-assembly followed by consecutive primary chain-microlayer-microframework assembly. A crystallochemically correct structure model was advanced for superionic LISICON Li₆Zn(GeO₄)₂ as a 2D analogue of Li₄GeO₄ containing only two types of voids in a layer, which are most likely to be sites for Li atoms to reside. A migration map was constructed to characterize the 2D set of conductivity channels in superionic LISICON.     

Geometrical and topological model of formation, selection, and evolution of precursor nanoclusters in the convergent matrix self-assembly mechanism of crystal formation

Combinatorial-topological analysis algorithms have been developed to reconstruct the code of convergent matrix self-assembly in the form of a sequence of significant elementary events e _i proceeding from structure data in a crystal-forming system that contains diverse structural units (atoms, molecules, and polyheral clusters). Mechanisms of selection of suprastructural units with maximal values of their connectivity indices to form chains from precursor clusters are considered. Two special cluster formation mechanisms are recognized. One is a linear mechanism where the number of particles is constantly increasing. The other is a discrete mechanism with an obligatory transiton of the evolving system to the matrix (complementary) selfassembly mode. Structure self-assembly follows the principle of the maximal filling of the crystal space and, accordingly, obeys the requirement for the maximal degree of complementary connectivity of precursor nanoclusters at all evolution steps. The model developed in this way has been used to interpret the formation and structural-topology specifics of carbon allotropes (fullerenes C60 and C70) and polymorphs of metals, H₂O (ice), silica, hydrido- and chlorosiloxanes, MEP clathrate family, some aluminosilicates (feldspar and zeolites), and C₂₀₄H₇₅₆Cl₃₆Mn₈₄O₄₆₂ (V = 20992 ?).     

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.     

Computer modeling of self-assembly of the crystal structure of zeolite Na384[Al384Si384O1536] (H2O)422 (LTN, cF4080) from suprapolyhedral cluster precursors AB 2 (A-K 48, B-K 24)

Combinatorial and topological analyses and a simulation of the self-assembly of zeolite crystal structure Na₃₈₄Al₃₈₄Si₃₈₄O₁₅₃₆ · 422H₂O (LTN, sp. gr. $Fd\bar 3$ ) have been performed using computer methods (TOPOS program package). A cubic cell with the parameters a = 36.95 ? and V = 50 449 ?³ contains 768 framework-forming AlO₄- and SiO₄ tetrahedra (T tetrahedra). The method of complete expansion of a 3D factor graph in nonintersecting cluster substructures in the tetrahedral T framework was used to reveal nanocluster precursors: A composed of 48 T tetrahedra (A-K₄₈) and B composed of 24 T tetrahedra (B-K₂₄). The nanocluster precursors A and B correspond to the polyhedral T clusters (tiles) 48T-grc and 24T-toc; they are involved in the matrix self-assembly of the crystal structure within the supracluster AB ₂. The centers of clusters A and B occupy the positions of Mg and Cu atoms in the Laves net AB ₂ = MgCu₂; i.e., the zeolite structure is a suprapolyhedral analog of an intermetallic compound. The self-assembly code of a 3D structure from complementary bound nanocluster precursors is completely reconstuctured in the following form: supracluster ?? primary chain ?? microlayer ?? microframework ?? ...framework. The localization of the Na⁺ template cations in the 6T- and 8T rings of nanocluster precursors A and B and Na⁺ spacer cations in the 28T-ltn tile with the formation of tetrahedral configuration and in the center of 6-ring, which arises as a result of bonding two B nanoclusters, is established.     

Assembly models for zeolite crystal structures according to the data of topological analysis by the tiling method

Cluster analysis of 194 tetrahedral T structures of zeolites has been performed by the tiling method using the TOPOS program package. An algorithm of the complete expansion of T structures in tiles (complementarily bound polyhedral clusters, which are responsible for the normal (face-to-face) partition of crystal space) and an algorithm for selecting nonintersecting tiles were used. Primary tiles, which number no more than two for any zeolite studied and have packing that completely determines the topology of the entire zeolite structure, have been determined for 41 zeolites. It is established that 24 zeolites are characterized by a single assembly version, 15 have two alternative versions, and IWR and TSC zeolites are characterized by 3 and 4 assembly versions. Isolated zeolites contain 2?C11 topologically different T _n tiles, where n is the number of tetrahedral T sites per tile; n = 4?C168 and the diameter is 6?C35 ?. The most numerous group of zeolites is characterized by n values of 4?C18. This group contains no tiles with the odd values n = 7?C17 and even value n = 6. The other group includes zeolites with large n values: 24, 30, 32, 36, 42, 48, 64, 72, 96, and 168.     

Hyperfine interactions in the Nd(Fe0.9Al0.1)2 alloy

The Nd(Fe_0.9Al_0.1)₂ alloy was synthesized at a high pressure. The crystalline structural characteristics of the alloy were determined. Hyperfine magnetic interactions in the range from 90 to 450 K were investigated using M?ssbauer spectroscopy and the temperature dependences of the magnetic characteristics of the alloy were established depending on the configuration of the nearest environment of the iron atom.     

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.     

Cluster self-organization of crystal-forming systems: Suprapolyhedral cluster precursors and self-assembly of the icosahedral structure of ZrZn<Subscript>22</Subscript>(<Emphasis Type="Italic">c</Emphasis>F184)

The mechanism of self-assembly of symmetrically and topologically different chains and microlayers (in the form of planar nets) from cyclic three-node clusters A ₃ is considered in the model system. The obtained nets correspond to the uninodal Shubnikov nets N 3 12 12 and N 3 6 3 6 and the new binodal net N1 3 6 3 6 + N2 3 3 6 6 (1: 2). A complete three-dimensional reconstruction of the self-assembly of the icosahedral structure of the ZrZn₂₂ compound (cF184) is performed using computer methods (with the TOPOS program package) according to the following scheme: cluster precursor → primary chain → microlayer → microframework (supraprecursor) → ... → framework. It is revealed that the suprapolyhedral cluster precursor (nanocluster ～12 Å in size) of the AB ₂ composition is formed by three polyhedra shared by vertices in a cyclic manner: the A-ZrZn₁₆ polyhedron (sixteen-vertex polyhedron with the point symmetry \(\bar 4\)3m) and two B-ZrZn₁₂ polyhedra (icosahedra with the point symmetry \(\bar 3\) m). The AB ₂ cluster precursor in the structure retains the symmetry m. It is established that the structural mechanism of self-assembly of the two-dimensional layer in the ZrZn₂₂ structure is described by the binodal net N1 3 6 3 6 + N2 3 3 6 6 (1: 2) constructed in the modeling.     

An Investigation of the Effects of X-Ray Treatment on the Concentration of Reducing Sugars in Potatos and Their Sprouting

This study investigates the effect of X-rays on potato tubers to stop their sprouting at different periods of storage. It has been found that there is a connection between the period of storage and the dose of irradiation. To control the quality of the irradiated tubers, the concentration of reducing sugars was measured during the entire experiment and compared to the parameters of non-irradiated potato tubers.