New Lanthanide Mixed-Valent Vanadium(III/IV) Oxosilicates, Ln4V5–xZnxSi4O22 (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 Ln4V5–xZnxSi4O22 (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. Ce4V4.77Zn0.23Si4O22, 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 Ln4V5–xZnxSi4O22 (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.一系列混合价态钒(III/IV)的镧系元素（lanthanide）氧硅酸盐（oxosilicates）Ln₄V₅₋ₓZnₓSi₄O₂₂（其中Ln代表La、Ce、Pr和Nd）通过高温熔盐法合成得到了高质量单晶体。以金属锌作为还原剂，成功实现了V(V)向V(III/IV)以及Ce(IV)向Ce(III)的原位还原，部分锌原子被掺入至晶体结构中。据我们所知，Ce₄V₄.₇₇Zn₀.₂₃Si₄O₂₂是首例含铈的混合价态钒硅酸盐。通过单晶X射线衍射（single-crystal X-ray diffraction）解析了其晶体结构，这四种同构氧硅酸盐均以契夫金石（chevkinite）结构型结晶，所属单斜空间群为I2/a。该系列Ln₄V₅₋ₓZnₓSi₄O₂₂（Ln=La、Ce、Pr、Nd）的晶胞与已报道的C2/m相Ln₄V₅Si₄O₂₂（Ln=La、Pr、Nd）相比，c轴加倍且失去了一个镜面。该三维晶体结构由以金红石（rutile）为结构基元的二维钒氧化物层与镧系氧化物层构成，两层之间通过Si₂O₇基团相互连接。测试了这些化合物的磁化率随温度的变化关系，仅含Nd的同系衍生物在5 K处出现磁相变；所有样品均在约130~150 K范围内出现磁化率曲线的不连续或线性偏离现象。