Comparative crystal chemical analysis of borophosphates and borosilicates

A comparative crystal chemical analysis of mixed borophosphate and borosilicate anionic radicals revealed the main difference between them: the condensation of [PO4] tetrahedra does not proceed via common vertices, whereas the sharing of vertices is possible for the [SiO4] tetrahedra. In all the borophosphates considered, phosphorus is found only in the formally isolated tetrahedra. The central part of the heterogeneous radicals is formed by tetrahedra of lower charge ions (B+3), and the tetrahedra that incrust the central part have higher valences (Si+4, P+5). In borosilicates, silicon forms its own constructions up to complex layers and frameworks because its charge (Si,4) is lower than that of phosphorus (P+5). The higher charge of phosphorus impedes two-dimensional and three-dimensional condensation. As a result, borophosphates form a variety of soro and chain radicals and only few layer and framework constructions.