Complex coordinated functional groups: A great genes for nonlinear optical materials

Complex coordinated functional groups [MA_xB_y] (M = Central coordination element; A, B = P, O, S, Se, F, Cl, Br or I) are composed of different types of anions A, B jointly linked to the same central cation M, which are in high potential to tune the physical properties of materials, e.g., second-order susceptibility, energy gaps and birefringence. Recently, Compound containing complex coordinated functional groups have attracted great attention in the nonlinear optical (NLO) field and a large number of this type crystals exhibit promising NLO performance. However, the inherent relationship between ionic group structure and optical properties of complex coordinated NLO materials have not been systematically studied. This article systematically summarizes complex coordinated NLO materials in recent five years from the perspective of the internal relationship between crystal structure and optical properties. In addition, we propose the ideal combination and arrangement modes for structural building units, and also reveal the influence of complex coordinated functional groups [MA_xB_y] toward the NLO response, optical band gap and phase matching ability of complex coordinated NLO materials.