A Series of Organic–Inorganic Hybrid Compounds [(C₂H₅)₄N]InCl_4–xBr_x (x = 0, 2, 4): Synthesis, Crystal Structure, and Nonlinear Optical Properties

A series of noncentrosymmetric (NCS) tetraethylammonium tetrahalide indium hybrids, [(C₂H₅)₄N]­InCl_4–xBr_x (x = 0, 2, 4), was synthesized by a hydrothermal reaction. Their structures, thermal properties, and linear and nonlinear optical properties were identified. The crystals belong to an isomorphic hexagonal system and feature zero-dimensional structures containing isolated distorted InCl_4–xBr_x^– tetrahedra with [N­(C₂H₅)₄]⁺ cations inserted as charge balance. On the basis of the powder second harmonic generation, the SHG levels of [(C₂H₅)₄N]­InCl_4–xBr_x (x = 0, 2, 4) were estimated to be approximately 0.5, 0.7, 0.8 × KDP, respectively. The relationship between halogen composition and band gap, optical anisotropy, and frequency doubling effects were evaluated by first-principles calculations, thus suggesting that halogen regulation favors the design of new organic–inorganic hybrid halides with excellent performances for many optoelectronic applications.