Mg assists in modulating the dimensionalities of the anionic frameworks of borates

Abstract

Three Mg-containing borates were obtained by high-temperature spontaneous crystallization. In the (A₂O)- or (A₂O-MO)-MgO-B₂O₃ system (A is alkali metal and M is alkaline-earth metal) reported in the ICSD, Li₄Mg₃SrB₁₂O₂₄ is the first compound that contains one-dimensional infinite anionic chains, and the two examples of the isostructural A₂Mg₃B₁₆O₂₈ (A = Rb, Cs) exhibit a two-dimensional infinite bilayer structure for the first time, which contributes to the enrichment of the structural chemistry of Mg-containing borates. Besides, the results of comparison and analysis in this system clearly show that Mg not only affects the anionic frameworks of borates to produce low-dimensional structures but, together with the ratio of N_cation/N_B, is responsible for the dimensionalities of the anionic frameworks in borates. The optical properties of the three compounds also show that they all have short cutoff edges, and Cs₂Mg₃B₁₆O₂₈, in particular, could reach the deep-ultraviolet region (<200 nm).