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.