Synthesis, Crystal Structure and Properties of the New Laminar Quaternary Tellurides SrLnCuTe3 (Ln = Sm, Gd–Tm and Lu)

 https://doi.org/10.3390/cryst13020291

This paper reports for the first time on the new laminar quaternary orthorhombic heterometallic quaternary tellurides SrLnCuTe₃, the fabrication of which has been a challenge until this work. Data on the crystal structure of tellurides complete the series of quaternary strontium chalcogenides SrLnCuCh₃ (Ch = S, Se, Te). Single crystals of the compounds were synthesized from the elements by the halogenide-flux method at 1070 K. The compounds are crystallizing in two space groups Pnma (Ln = Sm, Gd and Tb) and Cmcm (Ln = Dy–Tm and Lu). For SrSmCuTe₃ (a = 11.4592(7), b = 4.3706(3), c = 14.4425(9) Å, space group: Pnma) with the largest lanthanoid cation, Sr²⁺ shows C.N. = 7, whereas Sm³⁺ reveals a diminished coordination number C.N. = 6. For SrLuCuTe₃ (a = 4.3064(3), b = 14.3879(9), c = 11.1408(7) Å, space group: Cmcm) with the smallest lanthanoid cation, coordination numbers of six are realized for both high-charged cations (Sr²⁺ and Lu³⁺: C.N. = 6). The cations Sr²⁺, Ln³⁺, Cu⁺ each take independent positions. The structures are built by distorted [CuTe₄]^7– tetrahedra, forming the infinite chains {∞1[Cu(Te1)t1/1(Te2)t1/1(Te3)e2/2]5−}{∞1[Cu(Te1)1/1t(Te2)1/1t(Te3)2/2e]5−} along [010] in SrLnCuTe₃ (Ln = Sm, Gd and Tb) and [100] in SrLnCuTe₃ (Ln = Dy–Tm and Lu). The distortion of the polyhedra [CuTe₄]^7– was compared for the whole series SrLnCuTe₃ by means of τ₄-descriptor for the four coordinating Te^2– anions, which revealed a decrease in the degree of distortion with a decreasing radius at Ln³⁺. The distorted octahedra [LnTe₆]^9– form layers {∞2[Ln(Te1)2/2(Te2)2/2(Te3)2/2]3−}{∞2[��(Te1)2/2(Te2)2/2(Te3)2/2]3−}. The distorted octahedra and tetrahedra fuse to form parallel layers {∞2[CuLnTe3]2−}{∞2[Cu��Te3]2−} and between them, the Sr²⁺ cations providing three-dimensionality of the structure are located. In the SrLnCuTe₃ (Ln = Sm, Gd and Tb) structures, the Sr²⁺ cations center capped the trigonal prisms [SrTe₆₊₁]¹²⁻, united in infinite chains {∞1[Sr(Te1)2/2(Te2)3/3(Te3)2/2]4−}{∞1[Sr(Te1)2/2(Te2)3/3(Te3)2/2]4−} along the [100] direction. The domains of existence of the Ba₂MnS₃, BaLaCuS₃, Eu₂CuS₃ and KZrCuS₃ structure types are defined in the series of orthorhombic chalcogenides SrLnCuCh₃ (Ch = S, Se and Te). The tellurides SrLnCuTe₃ (Ln = Tb–Er) of both structure types in the temperature range from 2 up to 300 K are paramagnetic, without showing clear signs of a magnetic phase transition