Single crystals of Ln(3)Cl[SiS4](2) (Ln = La, Ce, Pr) were prepared by the reaction of lanthanide metal, sulfur, silicon and chlorine. Data collection was carried out using a STOE imaging plate detector at 293 K. The homologue compounds crystallize in the space group C2/c of the monoclinic system isotypically to Ln(3)X[SiS4](2) (X = Br, I) and the A-type of the halide oxosilicates Ln(3)X[SiO4](2) (X = Cl, Br; Ln = La, Ce, Pr) with four formula units in cells of dimensions: La3Cl[SiS4](2): a = 1567.2(3) pm, b = 777.8(2) pm, c = 1101.5(2) pm, beta = 96.88(2)degrees Ce3Cl[SiS4](2): a = 1559.4(3) pm, b = 770.2(2) pm, c = 1096.9(2) pm, beta = 97.07(2)degrees Pr3Cl[SiS4](2): a = 1555.9(3) pm, b = 764.2(1) pm, c = 1093.2(2) pm, beta = 97.40(2)degrees The corresponding residuals (all data) for the refined structures are 2.28% (La), 2.15% (Ce), and 3.17% (Pr), respectively. In the crystal structures, the chloride ions form chains along [0 0 1] with trigonal coordination by the lanthanide ions. (C) 2002 Elsevier Science Ltd. All rights reserved.