Effect of Rigid Units on the Symmetry of the Framework: Design and Synthesis of Centrosymmetric NaBa4(B5O9)2F2Cl and Noncentrosymmetric NaBa4(AlB4O9)2Br3

Two similarly stoichiometric borate halides, NaBa4(AlB4O9)(2)Br-3 and NaBa4(B5O9)(2)F2Cl, have been successfully designed and synthesized, and their structures were determined by single-crystal X-ray diffraction. Their crystal structures feature the [AlB4O9],, and [B5O9], networks, respectively. NaBa4(AlB4O9)(2)Br-3 is noncentrosymmetric and crystallizes in polar space group P4(2)nm, while NaBa4(B5O9)(2)F2Cl is centrosymmetric and crystallizes in monoclinic space group P2(1)/n. Powder second-harmonic generation (SHG) measurements reveal that NaBa4(AlB4O9)(2)Br-3 has an optical non-linearity comparable to that of KH2PO4 (ICDP) and is type I phase-matchable. In addition, infrared and UV-Vis-NIR diffuse reflectance spectroscopy, as well as electronic band structure calculations, were performed on the reported materials.