Two Sets of Metal Organic Frameworks along the Lanthanide Series Constructed by 2,3-Dimethylsuccinate: Structures, Topologies, and Strong Emission without Ligand Sensitization

Reactions
in aqueous solution under hydrothermal conditions between
(±)-2,3-dimethylsuccinic acid and lanthanide chlorides lead to
two different isostructural types with chemical formulas [Ln2­(C6H8­O4)3­(H2O)2] Ln­(III) = Pr–Eu (except
Pm) (Type I, compounds 1–4) and [Ln2­(C6H8­O4)3] Ln­(III) = Tb–Yb (except Tm) (Type II, compounds 5–9). The crystal structure has been solved
for the Pr (1)-, Sm (3)-, and Ho (7)-containing compounds by means of single-crystal XRD methods,
whereas powder XRD Rietveld refinement was used for the rest of the
MOFs. Compounds 1–4 crystallize in
the triclinic space group P1̅, whereas compounds 5–9 belong to the tetragonal space group P43212. Type I and II compounds are
3D frameworks consisting of chains of [LnO8­(H2O)] or [LnO8] polyhedra, respectively, linked by
dimethylsuccinate anions, giving rise to I1O2 connectivity. All the compounds were characterized by X-ray diffraction,
variable-temperature Fourier transform infrared spectroscopy, and
thermal analysis. An exhaustive topological study was performed in
comparison with other related compounds. The photoluminescent (PL)
properties for compounds 3, 4, and 5 have been also explored, indicating that a metal-centered
luminescent process takes place.

在水热条件下的水溶液中，(±)-2,3-二甲基琥珀酸与氯化镧系元素发生反应，得到两种不同的同构系列化合物，其化学式分别为[Ln₂(C₆H₈O₄)₃(H₂O)₂]（三价镧系元素Ln=Pr~Eu，Pm除外，记为I型，化合物1~4）与[Ln₂(C₆H₈O₄)₃]（三价镧系元素Ln=Tb~Yb，Tm除外，记为II型，化合物5~9）。通过单晶X射线衍射（X-ray Diffraction，XRD）技术解析了含Pr（化合物1）、Sm（化合物3）及Ho（化合物7）的化合物的晶体结构，其余金属有机框架（Metal-Organic Frameworks，MOFs）则采用粉末X射线衍射Rietveld精修进行结构表征。化合物1~4结晶于三斜晶系空间群P1̅，而化合物5~9则属于四方晶系空间群P4₃2₁2。I型与II型化合物均为三维框架结构，前者由[LnO₈(H₂O)]多面体链、后者由[LnO₈]多面体链通过二甲基琥珀酸根阴离子连接而成，形成I1O2连接拓扑。所有化合物均通过X射线衍射（XRD）、变温傅里叶变换红外光谱及热分析进行了表征。研究针对该系列化合物开展了全面的拓扑学分析，并与其他相关同类化合物进行了对比。此外，还对化合物3、4及5的光致发光（PL）性能进行了探究，结果表明其发光过程为金属中心发光机制。