Reticular chemistry-aided effective design of new second-order nonlinear optical selenites

Noncentrosymmetric (NCS) compounds are particularly important for modern optoelectronic technology, yet their rational structural design remains a great challenge. Herein, assisted by the idea of bottom-up reticular chemistry, seven new NCS selenites, AM₃[SeO₃]₂[Se₂O₅]₃ (A = K⁺/Rb⁺/Cs⁺; M = Al³⁺/Ga³⁺/In³⁺), have been successfully designed and synthesized by assembling main-group metal octahedral units and SeO₃ units, to construct honeycomb layers with regular channels to accommodate a variety of cations, and using planar hexagonal shapes to orientate the groups within the network. Based on this strategy, the overall symmetry of the solid-state compounds was effectively controlled, and by modifying locally connected atoms or groups, without disrupting the overall prototypical framework, a series of iso-reticular analogues have been obtained, which greatly increases the probability of NCS structures. Three of these compounds, CsM₃[SeO₃]₂[Se₂O₅]₃ were characterized experimentally and theoretically. The results show that they all have moderate second harmonic generation (SHG) responses, which are as large as that of commercial KH₂PO₄, and wide band gaps. Our study confirms the feasibility of reticular chemistry-assisted strategy in designing nonlinear optical materials with stable frameworks and good performance.