Promising Functional Structural Building Unit Trisulfimide (SO₂N)₃³– and Its Contributions to Second Harmonic Generation and Birefringence

A new functional structural building unit, trisulfimide ion (SO2N)33–, is reported. Its contributions to enhance the second harmonic generation (SHG) and birefringence (Δn) are discussed theoretically and experimentally, using two DUV transparent compounds, (NH4)2H(SO2N)3 (di-1, Cc, Eg, cal = 7.03 eV) and (NH4)3(SO2N)3 (tri-2, P21/c, Eg, cal = 6.89 eV). The acentric di-1 exhibits a phase-matching, strong SHG intensity (0.67 × KDP). And the Δn of di-1 (Δnobv = 0.016; Δncal = 0.018) is smaller than that of tri-2 (0.022obv; 0.023cal), and this variance arises from the fact that the coplanarity of the trisulfimide building units determines the Δn value. Moreover, theoretical studies utilizing real-space atom-cutting techniques indicate that H(SO2N)32– is the primary contributor to the SHG and Δn. These findings conclusively demonstrate that (SO2N)33–represents a novel functional structural building unit that offers an additional platform for exploring NLO and related materials.