A Challenge toward Novel Quaternary Sulfides SrLnCuS 3 (Ln = La, Nd, Tm): Unraveling Synthetic Pathways, Structures and Properties.

We report on the novel heterometallic quaternary sulfides SrLnCuS 3 (Ln = La, Nd, Tm), obtained as both single crystals and powdered samples. The structures of both the single crystal and powdered samples of SrLaCuS 3 and SrNdCuS 3 belong to the orthorhombic space group Pnma but are of different structural types, while both samples of SrTmCuS 3 crystallize in the orthorhombic space group Cmcm with the structural type KZrCuS 3 . Three-dimensional crystal structures of SrLaCuS 3 and SrNdCuS 3 are formed from the (Sr/Ln)S 7 capped trigonal prisms and CuS 4 tetrahedra. In SrLaCuS 3 , alternating 2D layers are stacked, while the main backbone of the structure of SrNdCuS 3 is a polymeric 3D framework [(Sr/Ln)S 7 ] n , strengthened by 1D polymeric chains (CuS 4 ) n with 1D channels, filled by the other Sr 2+ /Ln 3+ cations, which, in turn, form 1D dimeric ribbons. A 3D crystal structure of SrTmCuS 3 is constructed from the SrS 6 trigonal prisms, TmS 6 octahedra and CuS 4 tetrahedra. The latter two polyhedra are packed together into 2D layers, which are separated by 1D chains (SrS 6 ) n and 1D free channels. In both crystal structures of SrLaCuS 3 obtained in this work, the crystallographic positions of strontium and lanthanum were partially mixed, while only in the structure of SrNdCuS 3 , solved from the powder X-ray diffraction data, were the crystallographic positions of strontium and neodymium partially mixed. Band gaps of SrLnCuS 3 (Ln = La, Nd, Tm) were found to be 1.86, 1.94 and 2.57 eV, respectively. Both SrNdCuS 3 and SrTmCuS 3 were found to be paramagnetic at 20-300 K, with the experimental magnetic characteristics being in good agreement with the corresponding calculated parameters.