Syntheses, Crystal Structures, and Properties of Six New Lanthanide(III) Transition Metal Tellurium(IV) Oxyhalides with Three Types of Structures

Solid-state reactions of lanthanide(III) oxide (and lanthanide(III) oxyhalide), transition metal halide (and transition metal oxide), and TeO₂ at high temperature lead to six new lanthanide transition metal tellurium(IV) oxyhalides with three different types of structures, namely, DyCuTe₂O₆Cl, ErCuTe₂O₆Cl, ErCuTe₂O₆Br, Sm₂Mn(Te₅O₁₃)Cl₂, Dy₂Cu(Te₅O₁₃)Br₂, and Nd₄Cu(TeO₃)₅Cl₃. Compounds DyCuTe₂O₆Cl, ErCuTe₂O₆Cl, and ErCuTe₂O₆Br are isostructural. The lanthanide(III) ion is eight-coordinated by eight oxygen atoms, and the copper(II) ion is five-coordinated by four oxygens and a halide anion in a distorted square pyramidal geometry. The interconnection of Ln(III) and Cu(II) ions by bridging tellurite anions results in a three-dimensional (3D) network with tunnels along the a-axis; the halide anion and the lone-pair electrons of the tellurium(IV) ions are oriented toward the cavities of the tunnels. Compounds Sm₂Mn(Te₅O₁₃)Cl₂ and Dy₂Cu(Te₅O₁₃)Br₂ are isostructural. The lanthanide(III) ions are eight-coordinated by eight oxygens, and the divalent transition metal ion is octahedrally coordinated by six oxygens. Two types of polymeric tellurium(IV) oxide anions are formed:  Te₃O₈^4- and Te₄O₁₀^4-. The interconnection of the lanthanide(III) and divalent transition metal ions by the above two types of polymeric tellurium(IV) oxide anions leads to a 3D network with long, narrow-shaped tunnels along the b-axis. The halide anions remain isolated and are located at the above tunnels. Nd₄Cu(TeO₃)₅Cl₃ features a different structure. All five of the Nd(III) ions are eight-coordinated (NdO₈ for Nd(1), Nd(2), Nd(4), and Nd(5) and NdO₇Cl for Nd(3)), and the copper(I) ion is tetrahedrally coordinated by four chloride anions. The interconnection of Nd(III) ions by bridging tellurite anions resulted in a 3D network with large tunnels along the b-axis. The CuCl₄ tetrahedra are interconnected into a 1D two-unit repeating (zweier) chain via corner-sharing. These 1D copper(I) chloride chains are inserted into the tunnels of the neodymium(III) tellurite via Nd−Cl−Cu bridges. Luminescent studies show that ErCuTe₂O₆Cl and Nd₄Cu(TeO₃)₅Cl₃ exhibit strong luminescence in the near-IR region. Magnetic measurements indicate the antiferromagnetic interactions between magnetic centers in these compounds.