Noncentrosymmetric hybrid gallium halides built from non-polar inorganic units

Abstract

Hybrid organic–inorganic metal halide compounds are a versatile platform for developing materials for optoelectronic applications. In this report, we studied the crystal structures and optical properties of five hybrid noncentrosymmetric Ga³⁺ halides with tri- and tetraethylammonium cations. All new phases crystallize in polar space groups and contain isolated GaX₄⁻ units in their structures, which are charge-balanced by the corresponding organic cations. Different packing arrangements of structural units result in three distinct crystal systems for five new compounds: hexagonal, orthorhombic, and monoclinic. All new structures demonstrate SHG activity, varying from weak (0.13 × KDP) to strong (1.88 × KDP), which agrees with acentric structures of these Ga³⁺ phases. Although our attempts to relate the net dipole moments of the compounds with SHG response were unsuccessful, the coalignment of the GaX₄ tetrahedra is a likely structural prerequisite for the high SHG response observed in Et₄NGaCl₄. Overall, Ga hybrid halides provide a promising and flexible platform for the synthesis of new polar phases.