Photoluminescent 3D Lanthanide–Organic Frameworks Based on 2,5-Dioxo-1,4-piperazinylbis(methylphosphonic) Acid Formed via in Situ Cyclodehydration of Glyphosates

Hydrothermal reactions of lanthanide nitrates with glyphosate have resulted three new isostructural 3D lanthanide–organic frameworks, Ln­(NO3)­(H2L) [Ln = Eu (1), Tb (2), Gd (3); H4L = 2,5-dioxo-1,4-piperazinylbis­(methylphosphonic) acid], with good yields, where H4L as a new ligand was formed via in situ cyclodehydration of original ligand glyphosates during the hydrothermal reaction. The compounds were thoroughly characterized by IR, UV–vis, elemental analysis, single-crystal X-ray diffraction analysis, powder X-ray diffraction analysis, and thermogravimetric/differential thermal analysis (TG-DTA). Three compounds display 3D 6,6-connected open frameworks with 413·62 topology possessing 1D channels in which NO3– anions act as troglodytes by chelating Ln3+ centers. The TG-DTA study of the compounds showed remarkable thermal stability up to 380 °C. Under room temperature UV-light irradiation, the Eu3+ and Tb3+ compounds showed the corresponding characteristic Ln3+ intra 4fn emission peaks. The triplet energy level (21882 cm–1) of the ligand (H4L) was determined from the emission spectrum of its Gd3+ compound at 77 K. The emission lifetimes (1.54 ms of 5D0 for compound 1 and 1.98 ms of 5D4 for compound 2) and absolute emission quantum yields (10.1% for compound 1 and 5.9% for compound 2) were also determined.

以硝酸稀土盐与草甘膦（glyphosate）为原料进行水热反应，成功合成三例同构的三维稀土有机框架（lanthanide–organic frameworks）配合物，其通式为Ln(NO₃)(H₂L) [Ln = 铕(Eu, 1)、铽(Tb, 2)、钆(Gd, 3)；H₄L = 2,5-二氧代-1,4-哌嗪二(甲基膦酸)]，产物收率良好。反应过程中，原始配体草甘膦发生原位环脱水反应，生成新型配体H₄L。采用红外光谱(IR)、紫外-可见光谱(UV–vis)、元素分析、单晶X射线衍射分析、粉末X射线衍射分析以及热重-差热分析(TG-DTA)对上述配合物进行了全面表征。三例配合物均具有6,6-连接的三维开放骨架，拓扑类型为4¹³·6²，骨架内存在一维孔道；其中硝酸根阴离子通过螯合配位与Ln³+中心结合，填充于孔道内部。TG-DTA测试结果显示，该系列配合物可稳定存在至380 ℃，展现出优异的热稳定性。在室温紫外光激发下，铕配合物与铽配合物分别呈现出对应Ln³+的4f内层特征发射峰。通过测定钆配合物在77 K下的发射光谱，确定了配体H₄L的三重态能级为21882 cm⁻¹。同时测定了该系列配合物的发射寿命与绝对发射量子产率：配合物1的5D₀能级发射寿命为1.54 ms，配合物2的5D₄能级发射寿命为1.98 ms；配合物1的绝对发射量子产率为10.1%，配合物2为5.9%。