Synthesis, crystal structure and optical properties of a new beryllium borate, CsBe4(BO3)3

A novel beryllium borate CsBe4(BO3)3 has been grown in crystals by high-temperature flux method using spontaneous nucleation technique for the first time. The crystal structure of this compound was determined by single crystal X-ray diffraction analysis. It crystallizes in the orthorhombic space group Pnma with lattice parameters a = 8.3914(5) Å, b = 13.3674(7) Å, c = 6.4391(3) Å, Z = 4, V = 722.28(7) Å3. The crystal takes the same structure type as Rb analog based on the units of BO3 triangles and BeO4 tetrahedrons, displaying a three-dimensional tunnel structure with Cs atoms filling in the cages. The IR spectrum confirms the presence of BO3 groups and the UV–vis–IR diffuse reflectance spectrum exhibits this compound has a short UV cut-off edge below 200 nm. Band structures and density of states were calculated.

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► A new beryllium borate CsBe4(BO3)3 was synthesized and crystals were obtained by flux method.
► CsBe4(BO3)3 crystallizes in a new structure type.
► It exhibits a three-dimensional zeolite-like structure with Cs atoms filling in the cages.
► The basic structural units are [Be2BO4]− groups composed of BO3 and BeO4.
► The UV cut-off edge is below 200 nm.