γ-Brass Polyhedral Core in Intermetallics: The Nanocluster Model

Using the TOPOS program package, 26-atom nanoclusters of the \u3b3-brass (Cu5Zn8) type (0@4@22 or 0@8@18) were found in 5918 crystal structures of cubic intermetallics. The nanocluster models were built for all the intermetallics using a recently developed algorithm implemented into TOPOS. The relations of the structures based on the 0@4@22 core are explored as a result of migration of atoms between different shells of the nanoclusters. It is shown that the 0@4@22 nanoclusters frequently occur as building units of intermetallics of different composition and structure type. Regularities in chemical composition of 702 \u3b3-brass-type nanoclusters were found within both the nanoclusters approach (multishell structure) and the nested-polyhedra model. A database containing all topological types of \u3b3-brass nanoclusters is created with which one can search for the corresponding atomic configuration in any intermetallics

The Zeolite Conundrum : Why Are There so Many Hypothetical Zeolites and so Few Observed? A Possible Answer from the Zeolite-Type Frameworks Perceived As Packings of Tiles

In the attempt to explain why there are so many hypothetical zeolites and so few observed, a model of assembling zeolite-type frameworks as a packing of natural building units (smallest cages) and/or essential rings (smallest windows) is proposed. The packing units have no common T atoms, hence the model takes into account the process of polycondensation of T4+(OH)4 or [T3+(OH)4] 12 complex groups resulting in oligomeric TnOm(OH)k units, eliminating water molecules, and forming T 12O 12T bridges. The packings were modeled for all zeolite minerals and most of the synthetic zeolite-type frameworks accounting for 163 zeolites of the 201 known. It is shown that the extra-framework cations can play a role of templates for the packing units. Application of the model to 1220 hypothetical zeolites shows that only a small set could be explained as packing of tiles, suggesting a possible ranking of feasibility that may help to unravel the zeolite conundrum

New Types of Multishell Nanoclusters with a Frank\u2013Kasper Polyhedral Core in Intermetallics

A comprehensive study of the occurrence of two-shell clusters with the first shell as a Frank-Kasper polyhedron Z12, Z14, Z15, or Z16 (Frank-Kasper nanoclusters) is performed for 22951 crystal structures of intermetallics containing only metal atoms. It is shown that besides the familiar Bergman and Mackay clusters, two more types of high-symmetrical icosahedron-based nanoclusters are rather frequent; they both have a 50-atom second shell. Moreover, two types of high-symmetrical Frank-Kasper nanoclusters with a Friauf-polyhedron (Z16) core are revealed; these nanoclusters have 44 and 58 atoms in the second shell. On the contrary, Z14 and Z15 Frank-Kasper polyhedra have been found to be rare and improper to form distinct nanoclusters in crystals. The second shells of Frank-Kasper nanoclusters have been revealed possessing their own stability: they can be realized in nanoclusters with different internal polyhedra and can shift around the core shell. The role of Frank-Kasper nanoclusters in assembling intermetallic crystal structures is illustrated by several examples

Cellular automata and local order in the structural chemistry of the lovozerite group minerals

The structural chemistry of the lovozerite group of minerals is considered using concepts of coordination polyhedra, finite automata and local order. A formal language for these lovozerite-type structures is constructed and the concept of a genetic code for this structure family is suggested. Information and structure are seen to be dialectically interlinked