pH-Dependent Syntheses, Luminescent, and Magnetic Properties of Two-Dimensional Framework Lanthanide Carboxyarylphosphonate Complexes

A series of novel organic–inorganic complexes based on trivalent lanthanide and HOOC–C6H4–CH2PO­(OH)­(OC2H5) (H2L′) formulated as Ln­(HL)­(H2L)­(H2O) (H3L = HOOC–C6H4–CH2PO­(OH)2, Ln = La, 1; Ce, 2; Pr, 3; Nd, 4; Sm, 5; Eu, 6; Gd, 7; and Tb, 8) have been obtained as single phases by regulating the pH values under hydrothermal conditions. They are isomorphous and feature a network in which the LnO7 polyhedra are interconnected by bridging CPO3 tetrahedra into inorganic layers. These layers are further cross-linked by hydrogen bonds of the carboxyl acid groups of ligands into a S-shape pillared framework architecture. Luminescent measurements indicate that complexes 1–5 and 7 exhibit ligand-centered blue light emission bands. Complexes 6 and 8 display Ln-centered strong red and green luminescence, respectively. To elucidate the energy transfer process between ligands and metal ions, the energy levels of the relevant electronic states have been estimated. Simultaneously Eu3+ and Tb3+ were observed to accept energy with their several different 5Dj, resonance levels depending on the lowest triplet state energy level of the ligand. Magnetic properties of 7 and 8 have also been studied.本研究通过水热条件下调控pH值，成功制备得到一系列基于三价镧系元素与配体HOOC–C₆H₄–CH₂PO(OH)(OC₂H₅)（记为H₂L′）的新型有机-无机配合物，其化学式为Ln(HL)(H₂L)(H₂O)（其中H₃L = HOOC–C₆H₄–CH₂PO(OH)₂，Ln分别对应La(1)、Ce(2)、Pr(3)、Nd(4)、Sm(5)、Eu(6)、Gd(7)与Tb(8)），产物均为单相。该系列配合物均为同构结构，其骨架中七配位镧氧多面体通过桥连CPO₃四面体相互连接，形成无机层状结构。上述无机层进一步通过配体羧基形成的氢键相互交联，构筑为S型柱撑骨架架构。发光性能测试表明，配合物1~5与7均呈现配体中心的蓝光发射带；配合物6与8则分别展现出以镧系离子为中心的强红光与绿光发射。为阐明配体与金属离子间的能量传递过程，本研究估算了相关电子态的能级位置。同时观测到，Eu³+与Tb³+可借助自身多个不同的⁵Dⱼ共振能级接收配体传递的能量，该能量接收过程取决于配体的最低三重态能级。此外，本研究还对配合物7与8的磁学性能开展了表征研究。