Synthesis, structural characterization and optical properties of a new cesium aluminum borate, Cs2Al2B2O7

A new borate, Cs2Al2B2O7, was synthesized by solid-state reaction. It crystallizes in the monoclinic space group P21/c with a=6.719(1) Å, b=7.121(1) Å, c=9.626(3) Å, β=115.3(1)°, and Z=2. In the structure, two AlO4 tetrahedra and two BO3 planar triangles are connected alternately by corner-sharing to from nearly planar [Al2B2O10] rings, which are further linked via common O1 atom to generate layers in the bc plane. These layers then share the O3 atoms lying on a center of inversion to form a three-dimensional framework with Cs atoms residing in the channels. The IR spectrum confirms the presence of both BO3 and AlO4 groups and the UV–vis–IR diffuse reflectance spectrum indicates a band gap of about 4.13(2) eV.