Two Alkali Metal Borates Built by {Li@B 14 } and {B 15 } Cluster Units

Abstract

Two alkali metal borates, K7[{Li@B12O18(OH)4}{BO(OH)3}2] (1) and LiNa2K2[B15O25] (2), were successfully synthesized via mid-temperature hydrothermal methods. 1 features a Li-centered [{Li@B12O18(OH)4}{BO(OH)3}2]7- ({Li@B14}) cluster, forming a 3D supramolecular framework through hydrogen bonds. Notably, the {B14} cluster is reported for the first time, containing a [12:6Δ+6T]-configured [B12O18(OH)6]6- cluster terminally decorated with two BO(OH)3 tetrahedra. By varying the reactant concentrations and temperature based on 1, 2 was obtained, achieving the expansion of dimensionality. 2 exhibits a 3D open-framework templated by three kinds of distinct alkali metal ions (Li+, Na+, K+), and represents a rare example of B15O29-based framework obtained under hydrothermal conditions. The {B15} cluster is formed by a [12:4(3:2Δ+T)]-type [B12O24]12- cluster linked to a B3O7 ring. Both compounds exhibit ultraviolet (UV) cut-off edges and moderate birefringence, indicating promising potential for UV optical applications.