A selenite containing unusual [Ga2F(Se2O5)4(HSeO3)2]5- clusters with the polarization ‘lighted’ by F− anions

Rationally designing inorganic compounds with the specific functional property is still a great challenge. Herein, the first metal selenite Ga2(Se2O5)2(HSeO3)(H2SeO3)F containing three different kinds of Se–O groups and Ga(Se2O5)(HSeO3) have been successfully synthesized by the hydrothermal method. In Ga(Se2O5)(HSeO3), the polar GaO6 octahedra and Se–O groups arrange in opposite directions, resulting in its centrosymmetric (CS) crystal structure, whereas in Ga2(Se2O5)2(HSeO3)(H2SeO3)F, by combining the chemical tailoring with the structure-directing properties of F− anions, unprecedented lantern-like polar structural clusters [Ga2F(Se2O5)4(HSeO3)2]5- are constructed, and these clusters adopt well-ordered alignments along the c axis promoting its noncentrosymmetric (NCS) and polar structure. Structural analysis indicates that the bifunctional F− anion plays the importantly polar ‘lighted’ roles for designing and synthesizing NCS and polar material of Ga2(Se2O5)2(HSeO3)(H2SeO3)F. The electron densities of states (DOS) calculations suggest that the interaction between oxygen and selenite determines their band gaps and the introduction of large electronegative F− anions obviously widens the UV cut-off edge of Ga2(Se2O5)2(HSeO3)(H2SeO3)F. In addition, performance measurements including powder second-harmonic generation (SHG), thermal analysis and infrared and UV-vis-NIR diffuse reflectance spectroscopy were performed on the title compounds.