Synthesis, characterization, and properties of reduced europium molybdates and tungstates

Flux Crystal Growth of Lanthanide Tungsten Oxychlorides, La8.64W6O30.45Cl, Ce8.64W5.74O30Cl, and Ln8.33W6O30Cl (Ln = Pr, Nd): Structural Stability in the Presence of Extreme Cation and Anion Disorder

A series of lanthanide tungsten oxychlorides with compositions of La_8.64W₆O_30.45Cl, Ce_8.64W_5.74O₃₀Cl, Pr_8.33W₆O₃₀Cl, and Nd_8.33W₆O₃₀Cl was synthesized as single crystals via a high-temperature flux growth method. The reduction of Ce(IV) to Ce(III) was performed in the synthesis of Ce_8.64W_5.74O₃₀Cl using Zn metal as the reducing agent. All four compounds crystallize in the tetragonal space group P4₂/nmc with a highly disordered and rather unusual arrangement of Ln(III) and W(VI) cations. The three-dimensional crystal structure consists of a complex network of Ln cations occupying multiple coordination environments, including LnO₈ cubes. The level of complexity the disorder adds to the overall structure was considered using calculations for the total information content of the crystal. The temperature dependence of the magnetic susceptibility of Pr_8.33W₆O₃₀Cl and Nd_8.33W₆O₃₀Cl was measured, and both compounds exhibit paramagnetic behavior across the entire 2-300 K temperature range measured.

New Lanthanide Mixed-Valent Vanadium(III/IV) Oxosilicates, Ln4V(5-x)Zn(x)Si4O22 (Ln = La, Ce, Pr, and Nd), Crystallizing in a Quasi Two-Dimensional Rutile-Based Structure

A family of lanthanide mixed-valent vanadium(III/IV) oxosilicates Ln4V(5-x)Zn(x)Si4O22 (Ln = La, Ce, Pr, and Nd) was synthesized as high-quality single crystals via a high-temperature molten salt method. An in situ reduction of V(V) to V(III/IV) as well as of Ce(IV) to Ce(III) was achieved utilizing Zn metal as the reducing agent, some of which is incorporated into the crystal structure. Ce4V(4.77)Zn(0.23)Si4O22, to the best of our knowledge, is the first example of a cerium-containing mixed-valent vanadium silicate. The crystal structures were determined by single-crystal X-ray diffraction, and the four isostructural oxosilicates were determined to crystallize in the chevkinite-structure type in the monoclinic space group I2/a. The unit cells of the Ln4V(5-x)Zn(x)Si4O22 (Ln = La, Ce, Pr, and Nd) series are related to the reported C2/m phases Ln4V5Si4O22 (Ln = La, Pr, and Nd) by a doubling of the c-axis and a loss of a mirror plane. The three-dimensional crystal structure consist of two-dimensional rutile-based vanadium oxide and lanthanide oxide layers linked via Si2O7 groups. The temperature dependence of the magnetic susceptibility of these compounds was measured, and only the Nd analogue exhibited a magnetic transition at 5 K; all samples displayed a discontinuity or deviation from linearity at ca. 130-150 K.

High-Temperature Salt Flux Crystal Growth of New Lanthanide Molybdenum Oxides, Ln5Mo2O12 Ln = Eu, Tb, Dy, Ho, and Er: Magnetic Coupling within Mixed Valent Mo(IV/V) Rutile-Like Chains

Five new lanthanide molybdenum oxides containing mixed valent Mo(IV/V) rutile-like chains, Ln5Mo2O12 Ln = Eu, Tb, Dy, Ho, and Er, were prepared utilizing a high-temperature molten salt flux synthesis involving an in situ reduction utilizing metallic reducing agents. All five compounds were structurally characterized by single-crystal and powder X-ray diffraction methods and were found to crystallize in the monoclinic space group C2/m. The molybdates all contain rare infinite chains consisting of MoO2O4/2 edge-sharing octahedra. The chains exhibit alternating long and short separations between octahedra caused by the presence of Mo-Mo bonds to form Mo2O10 units containing one unpaired electron. The temperature dependence of the magnetic susceptibility of these compounds was measured, and antiferromagnetic ordering was observed in all cases.