Synthesis and crystal structures of four new bromo-chalcogenides: MnSbS 2Br, MnBiSe 2Br and two allotropic forms of MnSbSe 2Br. Crystal chemistry of the [formula omitted] family ( [formula omitted], Bi; [formula omitted], Se; [formula omitted], Br, I)

Abstract

Four new compounds, MnSbS 2Br, MnBiSe 2Br and two allotropic forms of MnSbSe 2Br, were synthesized by solid state reaction at 500–600 °C. Their crystal structures were determined by single crystal X-ray diffraction. MnSbS 2Br, isotypic with MnSbSe 2I, is monoclinic, space group C 2 / m (No 12), with unit cell parameters a = 12.669 ( 3 ) , b = 3.8509 ( 8 ) , c = 9.585 ( 2 ) Å , β = 91.00 ( 3 ) ° , V = 467.54 ( 3 ) Å 3 , Z = 4 , R = 0.0622 . MnBiSe 2Br and one form of MnSbSe 2Br, isotypic with MnSbS 2Cl, are orthorhombic, space group Pnma (No 62), with unit cell parameters a = 9.995 ( 2 ) / 10.005 ( 2 ) , b = 4.0275 ( 8 ) / 3.9720 ( 8 ) , c = 12.928 ( 3 ) / 12.871 ( 3 ) Å , V = 520.44 ( 3 ) / 511.46 ( 18 ) Å 3 , Z = 4 , R = 0.0421 / 0.0523 , respectively. MnSbSe 2Br presents a second allotropic form, orthorhombic, space group Pbam (No 55), with a = 10.046 ( 2 ) , b = 25.994 ( 5 ) , c = 3.9689 ( 8 ) Å , V = 1036.4 ( 1 ) Å 3 , Z = 4 , R = 0.0545 . This last structure is a 1:1 combination of the two previous types. The crystal chemistry of the Mn PnQ 2 X family is discussed, and its structural types compared with similar (FeUS 3) or homologous derivatives (pavonite series).