Halder Purbashree, Barman Nandini, Tarannum Ibtesham, Mukhopadhyay Subrata, Schwarz Björn, Singh Saurabh Kumar, Goura Joydeb
Department of Chemistry, Jadavpur University, Kolkata-700032, India.
Computational Inorganic Chemistry Group, Department of Chemistry, Indian Institute of Technology Hyderabad, Kandi, Sangareddy, Telangana-502284, India.
Dalton Trans. 2025 Sep 23;54(37):13879-13893. doi: 10.1039/d4dt02976c.
A series of homometallic tetranuclear Ln complexes, [Ln(μ-OH){pyC(OH)O}(OCCMe)] [{pyC(OH)O} = monoanionic -diol form of di-2-pyridyl ketone; Ln = Nd (1), Eu (2), Tb (3), Dy (4), Er (5) and Yb (6)], have been synthesized and characterized. The asymmetric unit of each of the tetranuclear derivatives comprises the dinuclear motif, [Ln(μ-OH){pyC(OH)O}(OCCMe)]. The core structure of this Ln family possesses two homometallic structural subunits, LnIII3O, which are further connected through the bridging μ-OH ligands. Mean plane analysis indicates that all the lanthanide centers lie in the same plane. There are two types of eight-coordinated lanthanide centers present. The shape analysis revealed that the Ln1 center possesses a distorted elongated trigonal bipyramidal geometry while the Ln2 center has a distorted Johnson elongated triangular bipyramidal geometry. Solid-state room temperature photoluminescence studies of 1-5 show the ligand center emission band at 306 nm when excited at 270 nm. Compound 1, when excited at 380 nm emits at 517, 624, and 724 nm. On the other hand, excitation at 360 nm of compound 3, leads to emission peaks at 489, 542, 583, 590, and 624 nm. These bands are due to the f-f transitions of the Tb(III) centers. For all complexes, the dependence of direct current (DC) and alternating current (AC) magnetization on temperature and magnetic field was measured. The magnetic anisotropy and magnetic relaxation mechanism were also studied using the complete active space self-consistent field (CASSCF) methodology for complexes 1-6. The SINGLE_ANISO module is used to extract the relevant spin-Hamiltonian parameters. We have calculated the magnetic exchange couplings (-) for all the complexes. For complexes 3 and 4, we observed a sizable tunnel splitting of 1.5 × 10 cm and 1.9 × 10 cm, indicating that QTM is still a dominant mechanism for magnetic relaxation in the exchange-coupled systems, resulting in diminished SMM behaviour.
一系列同金属四核镧系配合物，[Ln(μ-OH){pyC(OH)O}(OCCMe)] [{pyC(OH)O}=二-2-吡啶基酮的单阴离子二醇形式；Ln = Nd (1)、Eu (2)、Tb (3)、Dy (4)、Er (5) 和 Yb (6)] 已被合成并表征。每个四核衍生物的不对称单元包含双核基序，[Ln(μ-OH){pyC(OH)O}(OCCMe)]。这个镧系家族的核心结构拥有两个同金属结构亚基，LnIII3O，它们通过桥连的μ-OH配体进一步连接。平均平面分析表明所有镧系中心位于同一平面。存在两种类型的八配位镧系中心。形状分析表明，Ln1中心具有扭曲的拉长三角双锥几何形状，而Ln2中心具有扭曲的约翰逊拉长三角双锥几何形状。1-5的固态室温光致发光研究表明，当在270nm激发时，在306nm处有配体中心发射带。化合物1在380nm激发时在517、624和724nm处发射。另一方面，化合物3在360nm激发时导致在489、542、583、590和624nm处出现发射峰。这些带归因于Tb(III)中心的f-f跃迁。对于所有配合物，测量了直流（DC）和交流（AC）磁化强度对温度和磁场的依赖性。还使用完全活性空间自洽场（CASSCF）方法对配合物1-6研究了磁各向异性和磁弛豫机制。使用SINGLE_ANISO模块提取相关的自旋哈密顿参数。我们计算了所有配合物的磁交换耦合（-）。对于配合物3和4，我们观察到1.5×10 cm和1.9×10 cm的可观隧道分裂，表明QTM仍然是交换耦合系统中磁弛豫的主导机制，导致单分子磁体行为减弱。
