CeSbS 2 Br 2 (I), Ce 1/ 2 La 1/ 2 SbS 2 Br 2 (II), and LaSbS 2 Br 2 (III) have been synthesized at 7003C from a mixture of LnBr 3 , Ln 2 S 3 , Sb, and S and characterized by single-crystal X-ray di4raction. The three phases are isostructural (space group P2 1 /c, Z β«Ψβ¬ 4) and crystallize in a novel, dense, bidimensional structure with cell parameters a β«Ψβ¬ 8.709(3) A > , b β«Ψβ¬ 9.187(2) A > , c β«Ψβ¬ 17.397(5) A > , β«Ψβ¬ 104.26(3)3 for I, a β«Ψβ¬ 8.739(7) A > , b β«Ψβ¬ 9.219(7) A > , c β«Ψβ¬ 17.41(2) A > , β«Ψβ¬ 104.3(1)3 for II, and a β«Ψβ¬ 8.785(1) A > , b β«Ψβ¬ 9.236(2) A > , c β«Ψβ¬ 17.372(3) A > , β«Ψβ¬ 104.09(2)3 for III. In these compounds, [LnS 5 Br 4 ] and [LnS 3 Br 6 ] (Ln β«Ψβ¬ Ce, La) distorted tricapped trigonal prisms de5ne in5nite 2
[LnS 2 Br 2 ] layers counterbalanced and capped by antimony cations. In good accordance with the structural features, the charge balance in these materials is to be written Ln III Sb III S ΨII 2 Br ΨI 2 . These compounds exhibit a yellow hue with a measured absorption threshold of 2.42(1), 2.55(1), and 2.72(1) eV for I, II, and III, respectively. In the two cerium containing bromothioantimonates I and II, the origin of the color is assigned to a Ce+4fPCe+5d electronic transition, which shifts to higher energy from I to II due either to a matrix e4ect (increase of the mean Ln+S distances under the substitution of Ce for La) or to an atomic ordering between Ce and La cations on the Ln(1) and Ln(2) crystallographic sites. In contrast, the electronic transition at play in III involves a charge transfer from the bromine and sulfur ions to the antimony ions, the latter contributing substantially to the lowermost levels of the conduction band.