Laboratório de Síntese Inorgânica e Bioinorgânica, Instituto de Química, Universidade de Brasília, Brasília, DF, Brazil.
Laboratório de Bioinorgânica e Cristalografia (LABINC), Departamento de Química, Universidade de Santa Catarina, Florianópolis, SC, Brazil.
Spectrochim Acta A Mol Biomol Spectrosc. 2023 Aug 5;296:122677. doi: 10.1016/j.saa.2023.122677. Epub 2023 Mar 31.
Three new complexes Na[Ln(pic)]ּ⋅2.5HO (Ln = Tb, Eu or Gd; pic = picolinate) were synthesized and characterized by infrared spectroscopy, powder X-ray diffraction and thermogravimetric analyses. The molecular structures of the complexes have been determined by single-crystal X-ray diffraction. The three isostructural lanthanide complexes crystalize in the hexagonal system with space group P622 to Eu complex and Gd complex and space group P622 to Tb complex. In each of the complexes, the picolinate ligands are bonded to Ln and Na ions by different coordination modes promoting polymeric structures. The photoluminescent properties of complexes were studied and combined with theoretical studies using the density functional theory (DFT: B3LYP, PBE1PBE) and the semiempirical method AM1/Sparkle from the single crystal X-ray diffraction structures to assign a suitable model for describing the system. The B3LYP DFT functional was considered the most adequate for providing structural properties of the compounds and for describing luminescence properties. The excited triplet states (T) and excited singlet states (S) of the ligand were determined theoretically using Time-dependent DFT calculations (TD-DFT: B3LYP, CAM-B3LYP and LC-wPBE) and INDO/S-CIS, with the best agreement with experimental values obtained from the LC-wPBE DFT functional. The photoluminescent spectra of the complexes and their lifetime measurements were determined indicating that the Eu complex and Tb complex display different intramolecular energy transfer mechanisms with higher efficiency to ligand-to-terbium energy transfer. In addition, the experimental and theorical Judd-Ofelt intensity parameters and quantum yields of the complexes were also determined and discussed besides to a proposed 9-state diagram to describe the luminescence properties of the Eu complex. The low value of emission quantum efficiency of D emitting level of Eu(III) ion was explained by the presence of the ligand-to-metal charge transfer state (LMCT) evidenced experimentally and theoretically. A good agreement was obtained between the proposed kinetic model and experimental results showing the consistency of the set of rate equations assumed and the intramolecular pathways proposed.
三种新的配合物 Na[Ln(pic)]ּ⋅2.5HO（Ln = Tb、Eu 或 Gd；pic = 皮考啉酸）被合成并通过红外光谱、粉末 X 射线衍射和热重分析进行了表征。通过单晶 X 射线衍射确定了配合物的分子结构。三个同构的镧系元素配合物在六方晶系中结晶，Eu 配合物和 Gd 配合物的空间群为 P622，Tb 配合物的空间群为 P622。在每个配合物中，皮考啉酸配体通过不同的配位模式与 Ln 和 Na 离子键合，促进了聚合物结构的形成。研究了配合物的光致发光性质，并结合密度泛函理论（DFT：B3LYP、PBE1PBE）和单晶 X 射线衍射结构的半经验方法 AM1/Sparkle 进行了理论研究，以确定合适的模型来描述该体系。B3LYP DFT 函数被认为最适合提供化合物的结构性质和描述发光性质。配体的激发三重态（T）和激发单重态（S）通过时间相关的 DFT 计算（TD-DFT：B3LYP、CAM-B3LYP 和 LC-wPBE）和 INDO/S-CIS 进行了理论上的确定，与从 LC-wPBE DFT 函数获得的实验值吻合得最好。测定了配合物的光致发光光谱及其寿命测量值，表明 Eu 配合物和 Tb 配合物显示出不同的分子内能量转移机制，具有更高的效率的配体到铽能量转移。此外，还测定和讨论了配合物的实验和理论 Judd-Ofelt 强度参数和量子产率，以及提出了一个 9 态图来描述 Eu 配合物的发光性质。Eu(III)离子的发射量子效率低的原因是实验和理论上都证实了配体到金属电荷转移态（LMCT）的存在。所提出的动力学模型与实验结果吻合较好，表明所假设的一组速率方程和所提出的分子内途径是一致的。
