Chloride derivatives of lanthanoid(III) ortho-oxidotungstates(VI) with the formula LnCl[WO4] (Ln=Gd–Lu): Syntheses, crystal structures and spectroscopic properties

• The LnCl[WO4] series for Ln = Gd − Lu was synthesized as single phase materials.
• The facile solid-state synthesis comprises only easy-to-handle chemicals.
• The series displays a structural break between Er (CN = 8) and Tm (CN = 7).
• Luminescence properties of Eu3+ doped and bulk samples were investigated.
• The luminescence is visible despite the presence of usually quenching Cl− anions.

The lanthanoid(III) chloride ortho-oxidotungstates(VI) with the formula LnCl[WO4] crystallize monoclinically in space group C2/m (a=1019–1032, b=721–733, c=682–689 pm and β=107–108°, Z=4) for Ln=Gd–Er and triclinically in space group P1̄ (a=593–596, b=719–721, c=684–686 pm, α=93–94, β≈103 and γ≈122°, Z=2) for Ln=Tm–Lu. The monoclinic structure contains crystallographically unique Ln3+ cations, which are surrounded by two Cl− and six O2− anions forming distorted trigonal dodecahedra. Their fusion via common edges leads to anionic layers ∞2{[LnCl2/2eO4/2eO2/1t]6−}. The polyhedra around the Ln3+ cations in the triclinic crystal structure are also built up by two Cl−, but only five O2− anions to form distorted monocapped trigonal prisms. Their linkage through edges constitutes anionic strands ∞1{[LnCl2/2eO2/2eO3/1t]6−} along [100]. The complex anionic entities of both LnCl[WO4] arrangements become interconnected by W6+ cations to complete the structures by generating discrete [WO4]2− tetrahedra. Since the title compounds emerge as pure phases according to X-ray powder diffractometry, spectroscopic measurements such as single crystal Raman as well as diffuse reflectance spectroscopy (DRS) were performed. Furthermore, GdCl[WO4] and LuCl[WO4] are suitable host materials for doping with Eu3+, which leads to materials with a red luminescence upon excitation with UV light for both structures. Moreover, TbCl[WO4] exhibits a Tb3+-typical yellow-green bulk luminescence upon UV excitation, which could be analyzed by luminescence spectroscopy.

Layers consisting of edge-sharing Ln3+-centered anion polyhedra within the monoclinic structure type (top) versus strands of also edge-sharing Ln3+-centered anion polyhedra within the triclinic structure type of the LnCl[WO4] series (bottom).Figure optionsDownload as PowerPoint slide