pH Controlled Pathway and Systematic Hydrothermal Phase Diagram for Elaboration of Synthetic Lead Nickel Selenites

The PbO–NiO–SeO2 ternary system was fully
studied using constant hydrothermal conditions at 473 K. It yields
the establishment of the corresponding phase diagram using a systematic
assignment of reaction products by both powder and single-crystal
X-ray diffraction. It leads to the preparation of three novel lead
nickel selenites, α-PbNi­(SeO3)2 (I), β-PbNi­(SeO3)2 (II), and PbNi2(SeO2OH)2(SeO3)2 (III), and one novel lead cobalt selenite,
α-PbCo­(SeO3)2 (IV), which
have been structurally characterized. The crystal structures of the
α-forms I, IV, and III are based on a 3D complex nickel selenite frameworks, whereas the
β-PbNi­(SeO3)2 modification (II) consists of nickel selenite sheets stacked in a noncentrosymmetric
structure, second-harmonic generation active. The pH value of the
starting solution was shown to play an essential role in the reactive
processes. Magnetic measurements of I, III, and IV are discussed.

本研究在473 K的恒定水热条件下，对PbO–NiO–SeO₂三元体系开展了全面系统的探究。通过粉末X射线衍射与单晶X射线衍射对反应产物进行系统性物相归属，构建了该体系对应的相图。本研究成功制备出三种新型铅镍亚硒酸盐：α-PbNi(SeO₃)₂（标记为I）、β-PbNi(SeO₃)₂（标记为II）以及PbNi₂(SeO₂OH)₂(SeO₃)₂（标记为III），以及一种新型铅钴亚硒酸盐α-PbCo(SeO₃)₂（标记为IV），并对上述所有化合物完成了结构表征。其中α晶型I、IV与III的晶体结构均基于三维复合镍亚硒酸盐骨架；而β-PbNi(SeO₃)₂变体（II）则由镍亚硒酸盐片层堆叠形成非中心对称结构，具备二次谐波产生活性。实验证实，初始溶液的pH值对反应过程起到关键性作用。此外，本文还对化合物I、III与IV的磁学性能测试结果进行了讨论分析。