“…Hence, Hg-based chalcogenides may provide an attractive playground for IR-NLO materials (it should be mentioned that element Hg and most of the Hg-based compounds are extremely toxic and unfriendly to the environment; therefore, all the manipulations should be performed with great care). According to our investigation, only a few Hg-based metal chalcogenides have been reported as promising IR NLO materials including HgGa 2 S 4 , 20 BaHgQ 2 (Q = S, Se), 21,22 Li 2 HgMS 4 (M = Si, Ge, Sn), 23 Li 4 HgGe 2 S 7 , 24 and A 2 Hg 3 M 2 S 8 (A = Na, K; M = Si, Ge, Sn). 25,26 In particular, the [HgSe 3 ] 4− groups in BaHgSe 2 were identified as the first π-conjugated anionic groups with large NLO susceptibilities and stable chemical properties in IR NLO materials.…”