Two new quaternary chalcogenides, namely Ba4Ga4SnSe12 and Ba6Ga2SnSe11, have been synthesized for the first time, representing the first two members in the A/M/Sn/Q (A = alkaline–earth metal; M = Al, Ga, In; Q = S, Se, Te) system. Ba4Ga4SnSe12 crystallizes in the non−centrosymmetric space group P 21/c of the tetragonal system and has a three−dimensional structure. Its three−dimensional framework is built up from corner−sharing GaSe4 and SnSe4 tetrahedra with eight−coordinated Ba2+ cations residing in the cavities. Ba6Ga2SnSe11 crystallizes in a new structure type in the monoclinic centrosymmetric space group P21/c. The structure of Ba6Ga2SnSe11 features a zero–dimensional structure containing totally isolated distorted SnSe4 tetrahedra and discrete Ga2Se7 unit with Ba2+ cations located between them. On the basis of the diffuse-reflectance spectra, the band gaps are 2.45 (2) eV and 2.30 (2) eV for Ba4Ga4SnSe12 and Ba6Ga2SnSe11 respectively. In addition, electronic structure calculation on Ba4Ga4SnSe12 indicates that it is a direct−gap semiconductor with the band gap mainly determined by the [Ga4SnSe12]8− anionic framework. 

Dalton Trans., 2014