Stepwise fragmentation of coordination polyhedra [MXn]: Fragmentation of the [MO10] sphenocorona

The model of the stepwise fragmentation of coordination polyhedra is develo ped. The model is based on geometrical transformations of an n-vertex polyh edron involving (i) progressive removal of its vertices and (ii) symmetriza tion of the nascent fragments upon size averaging of its edges and faces. P articular trajectories of geometrical transformations are followed with the use of the fragmentation matrix. The validity of the model is verified by comparing the M-10 --> M-n model transformations to the [MO10] --> [MOn] po lyhedral transformations in the crystal structures of the compounds found i n the BaO(SrO)-Ln(2)O(3)-B2O3 and Ln(2)O(3)-GeO2-P2O5 systems. The stepwise fragmentation of coordination polyhedra results in the formation of multip olyhedral aggregates in the structures of lanthanide and Ba (Sr) compounds. The possible formation of multipolyhedral aggregates is suggested to be on e of the reasons for glass formation in similar systems.