“…During the past two decades, the exploration of new secondorder nonlinear optical (NLO) materials has attracted great academic interest due to their potential applications in photonic technologies, such as frequency conversion and signal communication. [1][2][3][4][5][6][7][8][9][10] For synthetic chemists, it is still a challenge to exploit new solid state materials with novel structures and fantastic properties, especially, second-order NLO materials with noncentrosymmetric (NCS) crystal structures. It has been demonstrated that introducing NLO active units can form materials with excellent second-harmonicgeneration (SHG) properties, including cations susceptible to second-order Jahn-Teller (SOJT), i. e. stereo-chemically active lone pair (SCALP) cations (Sn 2 + , Pb 2 + , Sb 3 + , Bi 3 + , Se 4 + , Te 4 + , I 5 + , etc) and d 0 transition metal cations (Ti 4 + , V 5 + , Nb 5 + , Mo 6 + , etc) in distorted polyhedral environments; or p-conjugated planar triangular units (BO 3 3À , CO 3 2À and NO 3 À ).…”