InO6X (X = Cl, Br): Distinct Functional Motif Family for Nonlinear Optical Materials
Functional motifs are essential microscopic units that govern the second harmonic generation (SHG) response in nonlinear optical (NLO) materials. While nonmetal-centered motifs have been extensively studied, metal-centered motifs with outstanding comprehensive performance remain scarce. Here, we report the successful synthesis of the first seven-coordinated indium oxy-chloride and oxy-bromide polyhedra, InO6X (X = Cl, Br), by leveraging the chelating and structure-directing properties of SeO3 groups. The InO6Br polyhedra exhibit the highest polarization anisotropy and hyperpolarizability among all reported indium oxy-chloride and oxy-bromide groups. Consequently, the first non-centrosymmetric halogenated indium selenites, In2(OH)(SeO3)2Cl (ISOC) and In2(OH)(SeO3)2Br (ISOB), were obtained. Both compounds demonstrate strong SHG intensity exceeding six times that of KDP (potassium dihydrogen phosphate) and wide band gaps greater than 4.0 eV, a combination rarely observed in inorganic selenites. This work presents a viable strategy for developing new NLO functional motifs and offers valuable insights for designing novel SHG materials with enhanced performance.