Boron Substructures in Inorganic Borides: Network Topology and Free Space

Abstract

We have analyzed polymeric boron substructures in all 1154 robust inorganic borides from the Inorganic Crystal Structure Database using topological and geometrical models as implemented in the ToposPro program package. We have classified all boron substructures into 63 topological types of atomic networks depending on the method of connection and discriminated them by periodicity into molecular, chain, layer, or framework motifs. We have revealed topological relations between boron motifs of different topologies and periodicities and found the boron substructures that can serve as templates for assembling motifs of a more complicated topology and/or a higher periodicity. We have applied the natural tiling approach to find all cages in a particular boron substructure and estimated the size of these cages with Voronoi polyhedra. The sizes of all metal atoms, which occur in the inorganic borides, have also been calculated in the same way. As a result, we have explained the composition of some borides and showed that the combined geometrical–topological approach helps one to estimate the feasibility of possible new boride structures and to refine the conditions for the synthesis or to prepare initial structural data for the subsequent predictive modeling.