Synthesis, crystal structure and topological features of microporous “anti-zeolite” Yb3(BO3)(OH)6∙2.1H2O, a new cubic borate with isolated BO3 groups

Abstract

Abstract A new cubic borate, Yb3[BO3](OH)6⋅2.1H2O was synthesized in a multi-component hydrothermal system Yb2(CO3)3: B2O3: P2O5 = 5 : 2: 1 (T = 280 °C; P = 90–100 atm; pH = 3). The crystal structure was studied using single crystal X-ray analysis. The structure has been refined in the space group I432, possesses the unit cell parameter a = 12.2808(15) A. A microporous positively charged framework is formed by predominant Yb cations coordinated by O2−, OH− as a tetragonal antiprism, which are linked together via common edges and vertices. The extra framework BO3 triangles center narrow channels, directed along 3-fold axis, are perpendicular to them and clamped between large Yb polyhedra. The large cavities with the effective cavity width 7.7 A are filled by disordered water molecules. The crystal chemical formula could be written as (Z = 8): |(BO3)(H2O)2.1|[Yb3(OH)6]. A topological analysis was performed using the ToposPro software. The framework is characterized by the following tile sequence: [34]6[324.46.68]; the calculated structural complexity parameters are: v = 48 atoms, IG = 1.500 bits/atom, and IG,total = 72.000 bits/unit cell; the framework density is 12.96 Yb/1000 A3. The Yb-borate is similar to the tetragonal compounds with the general formula ABa12(BO3)7F4 (A = Li, Na) and LixNa1-xBa12(BO3)7F4, which are characterized by co-called “anti-zeolite” frameworks, formed by Ba2+ cations. The excess of water in the structure of the new borate compound Yb3[BO3](OH)6⋅2.1H2O is determined by its zeolitic nature and by hydrothermal growth conditions.