Cluster self-organization of inorganic crystal-forming systems: Templated nanocluster precursors and self-assembly of framework MT structures of A/B,Zr silicates (A = Na, K; B = Ca, Sr)

Abstract

The basic concepts that are used to describe crystallization as a phenomenon of the hierarchical (cluster) self organization of a chemical system are considered. The templation of theoretically possible nan ocluster precursors composed of M octahedra and T tetrahedra by atoms of (A) alkaline and (B) alkaline earth metals is considered for the first time. A relationship between the A/B,M,T composition of templated nano cluster precursors with the composition of A/B,M silicates is established. The model that is developed is used to search for nanocluster precursors in framework MT structures of A/B,Zr silicates. Computer methods (TOPOS 4.0 program package) were used to perform complete 3D reconstruction of the self assembly of all (four) structural types of A/B,Zr silicates (A = Na, K; B = Ca, Sr) with frameworks of the MT 2 O 7 type: nan ocluster precursor -primary chain -microlayer -microframework . The invariant type of mono cyclic nanocluster precursor M 2 T 4 (with the point symmetries⎯ and 2), stabilized by one or two template cations (A and B), is determined. Bifurcations of the paths of evolution at the level (structural branching point) are established for the self assembly of the following frameworks: MT 1 in CaZrSi 2 O 7 (gittinsite, C2), MT 2 in SrZrSi 2 O 7 (P2 1 /c); MT 3 in Na