M3S2Cl5 (M = Nd, Dy): Two types of neodymium and dysprosium sulfide chlorides with double chains (1)(infinity){[S2M3](5+)} of edge-sharing [SM4] tetrahedra

Nd3S2Cl5 (monoclinic, P2(1)/c; a = 2176.9(2), b = 654.62(6), c = 703.91(7) pm, beta = 97.879(8)degrees; Z = 4) and Dy3S2Cl5 (orthorhombic, Pnma; a = 6 82.34(7), b = 2153.2(2), c = 638.21(6) pm; Z = 4) are formed by reacting ne odymium or dysprosium metal with sulfur and the respective trichloride (MCl 3) in suitable molar ratios (M:S:MCl3 = 4 : 6 : 5) within ten days in evacu ated silica tubes at 850 degreesC. The crystal structure of Dy3S2Cl5 (P2(1) /n 2(1)/m 2(1)/a) can be transferred to that of Nd3S2Cl5 (P1 1 2(1)/a equiv alent to P1 2(1)/c 1) through a lattice-equivalent transition of the index 2 (t2) by the loss of two screw axes, one diagonal glide plane, and one sim ple mirror plane. The moisture sensitive, transparent, pale violet (Nd3S2Cl 5) or faint yellow (Dy3S2Cl5) sulfide chlorides both exhibit infinite doubl e strands (1)(infinity){[S2M3](5+)} (M = Nd, DY) as main structural feature , which can be built of two condensed anti-SiS2-analogous chains of trans-e dge sharing [SM4] tetrahedra. These are running parallel [001] in Nd3S2Cl5 or [100] in Dy3S2Cl5 and arrange as a hexagonal closest packing of rods. Th e coordination polyhedra about the M3+ cations can be described as bicapped trigonal prisms (CN = 8) in both crystal structures, where by the collapse of two symmetrically equivalent particles the total number of three in the case of Nd3S2Cl5 is reduced to two crystallographically different ones in Dy3S2Cl5 Correspondingly, only three independent Cl- anions are present in the crystal structure of Dy3S2Cl5 for charge compensation and three-dimensi onal cross-linkage of the (1)(infinity){[S2M3](5+)} strands as compared to five in Nd3S2Cl5. The analogue holds for the S(2-)anions: The two distinct ones in the monoclinic Nd3S2Cl5 structure unite to a single one in orthorho mbic Dy3S2Cl5.