Solvothermal Syntheses and Characterizations of Two New Sliver Selenidoantimonates of Ag3SbSe3 and Ag5SbSe4

Two new sliver selenidoantimonates,namely,Ag3SbSe3 and Ag5SbSe4,were prepared under mid solvothermal conditions and structurally characterized by single-crystal X-ray diffraction studies.Ag3SbSe3 crystallizes in the orthorhombic space group Pnma（No.62） with a =8.2414（12）,b = 11.4925（17）,c = 21.220（3） A,V= 2009.8（5） A3 and Z= 12.Its structure belongs to the β-Ag3AsSe3 type and features a 3D complex network composed of distorted trigonal planar AgSe3 and tetrahedral AgSe4 units as well as SbSe3 trigonal pyramids.Ag5SbSe4 crystallizes in the orthorhombic system,nocentrosymmetric space group Cmc21（No.36） with a = 8.1148（6）,b =12.9829（10）,c = 8.7017（7） A,V= 916.76（12） A3 and Z = 4.Its structure adopts the Ag5SbS4 type and features a 3D framework based on trigonal planar AgSe3 units and SbSe3 trigonal pyramids.The results of optical absorption spectra and band structure calculations indicate that the title compounds are narrow band-gap semiconductors.