Oxysulfide chlorides, M4OS4Cl2, of the lanthanides (M = La - Nd) are obtained upon the oxidation of the metals with sulfur in the presence of MOCl (or M2O3) and MCl3 in appropriate molar ratios. Additional NaCl or an excess of MCl3 serving as a flux provide even single crystalline material after reactions at 850 °C for seven days in sealed tantalum capsules. The crystal structure of M4OS4Cl2 (hexagonal, P63mc, no. 186, Z = 2; M = La: a = 933.19(3), c = 701.22(4) pm, c/a = 0.7514, R = RH = 0.020; M = Ce: a = 925.49(3), c = 694.13(3) pm, c/a = 0.7500; M = Pr: a = 919.72(4), c = 688.53(4) pm, c/a = 0.7486; M = Nd: a = 914.25(4), c = 683.12(4) pm, c/a = 0.7472, R = 0.022, Rw = 0.019) contains isolated O2--centered (M3+)4 tetrahedra which are surrounded by twelve S2- and six Cl-, capping vertices, edges, and faces of each tetrahedron and linking to other [OM4] units. Basically, the structure is identical to that of Ba4OCl6 if Ba2+ is substituted by M3+ and 2/3 of the CL- anions are replaced by S2- to secure charge neutrality in M4OS4Cl2. Different models for the Cl-/S2- replacement are presented on the basis of comparisons of the Madelung part of the lattice energy (MAPLE) with the MAPLE sum of the binaries (M2O3, M2S3, and MCl3)
