Polysulfide Anions [Sx]2− (x = 2, 3, 4, 5): Promising Functional Building Units for Infrared Nonlinear Optical Materials

Infrared nonlinear optical (IR NLO) materials play significant roles in laser technology. The novel functional building units (FBUs) are of great importance in constructing NLO materials with strong second harmonic generation (SHG). Herein, polysulfide anion [S