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)

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 nanocluster 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 O-2(7) type: nan-ocluster precursor S (3) (0) -primary chain S (3) (1) -microlayer S (3) (2) -microframework S (3) (3) . The invariant type of mono-cyclic nanocluster precursor M (2) T (4) (with the point symmetries (1) over bar and 2), stabilized by one or two template cations (A and B), is determined. Bifurcations of the paths of evolution at the S (3) (1) level (structural branching point) are established for the self-assembly of the following frameworks: MT-1 in CaZrSi2O7 (gittinsite, C2), MT-2 in SrZrSi2O7 (P2(1)/c); MT-3 in Na2ZrSi2O7 (parakeldyshite,), K2ZrSi2O7 (khibinskite, P2(1)/b), and K2ZrGe2O7 (C2/c); and MT-4 in Na2ZrSi2O7 (H2O)(C2/c), Na3ScSi2O7 (Pbnm), and K3ScSi2O7 (P6(3)/mmc).