Chacogenides have attracted considerable interest because of their diverse structural features and their useful physical properties, such as second-order nonlinear optical properties.

The research group headed by Prof. CHEN Ling at Fujian Institute of Research on the Structure of Matter (FJIRSM), Chinese Academy of Sciences (CAS), has made significant progress on the design and synthesis of novel quaternary chalcogenides exhibiting strong nonlinear optical (NLO) response in middle-IR.

They successfully prepared seven new noncentrosymmetric (NCS) compounds of Ln₄GaSbS₉ (Ln = Pr, Nd, Sm, Gd–Ho) in which the bimetallic polar Sb₂S₅ units and dimeric (GaS₄)₂ tetrahedra are in-phase aligned as an infinite single anionic chain of {[(Ga₂S₆)(Sb₂S₅)]^10–}_∞ that is further packed in an NCS pseudolayer motif. Significantly, the Sm₄GaSbS₉ exhibits the strongest powder second harmonic generation (SHG) responses among sulfides to date with the intensity about 3.8 times that of benchmark AgGaS₂ at 2.05 μm laser radiation. The distortion of GaS₄ tetrahedra is small and the asymmetric units Sb₂S₅ are aligned at the same direction. A lobelike isosurface near each Sb³⁺ ion is observed from isosurface plot of the electron localization function (ELF) which indicates that the lone pairs on Sb³⁺ ion are stereochemically active, and the stereochemically active lone pair on Sb³⁺ ion is driven by the Sb–S bonding interactions. (J. Am. Chem. Soc. 2011, 50, 4617–4624) 

This research provides a valuable method in designing new NLO materials with suitable properties.

(Infinite chains of {[(Ga₂S₆)(Sb₂S₅)]^10–}_∞ and SHG responses of Sm₄GaSbS₉, Ho₄GaSbS₉ and AgGaS₂. The pink arrows show the in-phase alignment of such chains)