Acentric Organic-Inorganic Hybrid Halide [N(CH3)4]2HgBr2I2 Featuring an Isolated [HgBr2I2]2- Tetrahedron and Second-Order Nonlinearity.

A new hybrid compound [N(CH3)4]2HgBr2I2, obtained by a hydrothermal reaction, crystallized in the noncentrosymmetric space group P212121. Its structure contains an isolated asymmetric [HgBr2I2]2- tetrahedron with net polarization, connected by hydrogen bonds to form pseudo-one-dimensional chain structures. Moreover, its optical band gap, nonlinear optical (NLO) property, fluorescence property, and thermal property were characterized in detail. A rare high-temperature phase transition was observed in the compound. In addition, theoretical calculations were performed to elaborate the relation between electronic state, band structure, and their nonlinear optical response. These results indicate that [N(CH3)4]2HgBr2I2 is a new potential candidate for future photoelectronic applications in fluorescence and nonlinear optics.