Synthesis and characterization of a new borate Ba6Al4B14O33 with building blocks of AlO4, Al4O14, BO3, B6O14, and B6O13

Abstract

A new barium aluminoborate, Ba6Al4B14O33, has been synthesized by the high-temperature solution reaction at 700°C. The single-crystal XRD analysis showed that it crystallizes in a new structure type with space group P1¯, a=7.0070(14)Å, b=13.880(3)Å, c =14.702(3)Å, α=86.48(3)°, β=88.99(3)°, γ=83.46(3)°, V=1417.8(5)Å3, and Z=2. The fundamental building blocks in this structure are AlO4 tetrahedra, BO3 triangles, [Al4O14]16− groups composed of two AlO4 tetrahedra and two AlO5 trigonal bipyramids, [B6O14]10− groups formed by one BO3 triangle bonded to one [B5O12]9− double ring, and [B6O13]8− groups consisting of one BO3 triangle linked to one [B5O11]7− double ring. They are held together via common O atoms to form a 3D network, with intersecting open channels accommodating Ba2+ cations. The existence of both BO3 and BO4 groups is confirmed by FT-IR spectrum and an optical band gap of 3.44eV is obtained from UV–VIS diffuse reflectance spectrum. Solid-state fluorescence spectrum has also been studied exhibiting the maximum emission peak at around 527nm. Band structure calculations by the density functional theory method indicate that it is a direct band-gap insulator.