Cluster self-organization of TR-Containing germanate systems:: Suprapolyhedral precursors and self-assembly of the crystal structures of the LiNdGeO4 and CeGeO4 compounds

A combinatorial-topological analysis of the ortho-erinanates LiNdGCO(4) (space group Pbcn) and CeGeO4 (space group I 4(1)/a, the scheelite structure type), which have MT frameworks composed of polyhedral structural units in the form of M dodecahedra (NdO8 and CeO8) and T tetrahedra (GeO4), is performed using C the method of coordination sequences with the TOPOS pro-ram package. It is established that the structures of both orthog ermanates are characterized by equivalent crystal-forming nets 4444. The cluster precursors of the M2T2 cyclic type are identified by the method of two-color decomposition. The local symmetry of four-polyhedral clusters corresponds to the point group 2. In the precursor of the LiNdGeO4 orthogermanate, the Li atom is located above the M,T, ring. The number of Li-O bonds in this precursor is 4. The cluster precursors M2T2, and LiM2,T-2 are responsible for the formation of crystal -forming no clusters of a higher level according to the mechanism of matrix self-assembly. The coordination numbers of the cluster precursors in two-dimensional nets for these structures are found to be equal to 4. The equivalent bilayer TR,Ge stacks that consist of eight cluster precursors are revealed in the structures under investigation. It is demonstrated that there exist three types of translational interlayer arrangements of cluster precursors upon the formation of macrostructures of the orthogermanates.