The crystal chemical analysis of the class of borates has been carried out using the extended Dornberger-Schiff order–disorder (OD) theory based on the recognition of building blocks of various dimensions. All of the borate structures are built from several fundamental building blocks typical for every group of hexa-, penta-, tetra-, tri-, diborates; polyborates contain combinations of these different units. Zero dimensional periodic blocks and the fundamental building blocks in the Christ, Clark, and Strunz systems are in fact the same. Every block possesses its own topology and local symmetry. Consecutive condensation of blocks to rods, layers and frameworks is governed by symmetry laws, that is together with the local symmetry of units the subject of OD-analysis. For all borate groups considered, symmetry groupoids of various ranks have been proposed for different condensation units. Structural-generic branches for borates have been distinguished, hypothetical structural variants predicted, and the positions of compounds in the Strunz system either confirmed or corrected. Successful application of symmetry-topological principles of extended OD-theory to the borates gives a tool for crystal chemical analysis of many other compound classes.

A new polar hexaborate, K₃[B₆O₁₀]Br (space group R3m), is synthesized under hydrothermal conditions. The radical anion is composed of macallisterite hexaborate blocks 6[3Δ + 3T] formed by boron triangles and boron tetrahedra. The blocks are joined together through vertices into a [B₆O₁₀] _∞∞∞ ²⁻ zeolite-like framework of a new type. Large K⁺ cations and Br⁻ anions are located in extended channels that are aligned parallel to rhombohedral translations of the crystal lattice. The structure of the sublattice formed by large ions consists of BrK₆ bromo-centered octahedra, which are linked together through vertices into a hexagonally distorted perovskite framework. The perovskite framework is inserted into the boron-oxygen framework so that these two frameworks do not intersect. The nonlinear optical properties of powdered samples of the K₃[B₆O₁₀]Br compound are investigated using the second harmonic generation method. It is found that the K₃[B₆O₁₀]Br compound exhibits a high nonlinear optical activity that exceeds the activities of the majority of borate compounds and is characteristic of haloid borates of the hilgardite family.