Syntheses and Crystal Structures of CsCuNd 2 Se 4 and CsCuGd 2 Te 4 : Two Non ‐Isotypical Cesium Copper Lanthanide Chalcogenides with {}^1_\infty {[Cu Ch 3 ] 5– } Chains of Vertex‐Shared [Cu Ch 4 ] 7– Tetrahedra

The new chalcogenides CsCuNd 2 Se 4 and CsCuGd 2 Te 4 with analogous formulae were prepared from the elements by a flux method with CsCl as fluxing agent and cesium source. CsCuNd 2 Se 4 crystallizes in the orthorhombic space group Cmcm (no. 63) with four formula units per unit cell ( a = 424.69(3), b = 1475.81(8), c = 1465.42(8) pm), whereas CsCuGd 2 Te 4 is monoclinic with the space group C 2/ m (no. 12) and twelve formula units per unit cell ( a = 3764.75(19), b = 436.70(2), c = 2105.37(11) pm, β = 107.423(4)°). Both crystal structures feature three‐dimensional arrangements of the lanthanide and coinage metal cations along with the chalcogenide anions according to {}^3_\infty {[Cu Ln 2 Ch 4 ] – } ( Ln = Nd or Gd, Ch = Se or Te), leaving channels behind, in which the Cs + cations are incorporated. Hereby, vertex‐linked [Cu Ch 4 ] 7– tetrahedra join to form {}^1_\infty {[Cu Ch 3 ] 5– } chains in both cases. Whereas for the CsCuNd 2 Se 4 structure, these chains ( {}^1_\infty {[CuSe 3 ] 5– }) are embedded into a three‐dimensional network, erected by edge‐ and vertex‐linked [NdSe 6 ] 9– octahedra, which form corrugated layers further connected by common edges, in CsCuGd 2 Te 4 a different three‐dimensional {}^3_\infty {[Gd 2 Te 4 ] 2– } framework arises, comprising {}^1_\infty {[CuTe 3 ] 5– } chains, as well as vertex‐ and edge‐linked [GdTe 6 ] 9– octahedra. The major difference of the structures originates from the channels, in which the Cs + cations are located. In the tunnels of CsCuNd 2 Se 4 , the Cs + cations exhibit a bicapped trigonal prismatic selenide coordination, whereas in CsCuGd 2 Te 4 with two Cs + cations in one channel, they show bicapped trigonal prisms, as well as monocapped cubes of telluride anions as coordination spheres.