Chemical and Structural Evolution in the Th–SeO32–/SeO42– System: from Simple Selenites to Cluster-Based Selenate Compounds

While extensive success has been gained in the structural chemistry of the U–Se system, the synthesis and characterization of Th-based Se structures are widely unexplored. Here, four new Th–Se compounds, α-Th­(SeO3)2, β-Th­(SeO3)2, Th­(Se2O5)2, and Th3O2(OH)2(SeO4)3, have been obtained from mild hydrothermal or low-temperature (180–220 °C) flux conditions and were subsequently structurally and spectroscopically characterized. The crystal structures of α-Th­(SeO3)2 and β-Th­(SeO3)2 are based on ThO8 and SeO3 polyhedra, respectively, featuring a three-dimensional (3D) network with selenite anions filling in the Th channels along the a axis. Th­(Se2O5)2 is a 3D framework composed of isolated ThO8 polyhedra interconnected by [Se2O5]2– dimers. Th3O2(OH)2(SeO4)3 is also a 3D framework constructed by octahedral hexathorium clusters [Th6(μ3-O)4(μ3-OH)4]12+, which are interlinked by selenate groups SeO42–. The positions of the vibrational modes associated with both SeIVO32– and SeVIO42– units, respectively, were determined for four compounds, and the Raman spectra of α- and β-Th­(SeO3)2 are compared and discussed in detail.尽管铀-硒（U–Se）体系的结构化学研究已取得丰硕进展，但基于钍（Th）的硒结构的合成与表征仍鲜有探索。本文通过温和水热或低温（180–220 ℃）助熔剂法，成功合成了四种新型钍-硒化合物：α-Th­(SeO3)2、β-Th­(SeO3)2、Th­(Se2O5)2与Th3O2(OH)2(SeO4)3，并对其进行了系统的结构与光谱表征。α-Th­(SeO3)2与β-Th­(SeO3)2的晶体结构分别以ThO8多面体和SeO3多面体为结构基元，构建出三维（3D）网络结构，亚硒酸根阴离子沿a轴方向填充于钍原子构成的通道内。Th­(Se2O5)2为三维骨架结构，由孤立的ThO8多面体通过[Se2O5]2–二聚体相互连接构筑而成。Th3O2(OH)2(SeO4)3同样为三维骨架结构，其构建基元为八面体构型的六钍簇[Th6(μ3-O)4(μ3-OH)4]12+，该簇通过硒酸根SeO42–相互交联。本文确定了四种化合物中分别对应四价亚硒酸根（SeIVO32–）与六价硒酸根（SeVIO42–）单元的振动模式位置，并对α-Th­(SeO3)2与β-Th­(SeO3)2的拉曼光谱进行了详细对比与讨论。