Kalita Pankaj, Nayak Prakash, Ahmed Naushad, Herrera Juan Manuel, Venkatasubbaiah Krishnan, Colacio Enrique, Chandrasekhar Vadapalli
School of Chemical Sciences, National Institute of Science Education and Research Bhubaneswar, HBNI, Jatni, Khurda - 752050, Odisha, India.
Tata Institute of Fundamental Research Hyderabad, Gopanpally, Hyderabad-500 046, India.
Dalton Trans. 2020 Nov 10;49(43):15404-15416. doi: 10.1039/d0dt03054f.
The reaction of a bulky acetyl acetone ligand 1,3-dimesitylpropane-1,3-dione (MesacacH) with hydrated lanthanide chlorides in the presence of tetramethylammonium hydroxide afforded a new family of neutral mononuclear LnIII complexes [Ln(Mesacac)3(DMF)] (Ln = Dy (1); Tb (2); Y0.91Dy0.09 (3); and Er (4)). The molecular structures of these complexes were confirmed by single crystal X-ray diffraction studies. The coordination geometries of the LnIII centre were analysed by SHAPE analysis which revealed a capped octahedral geometry in 1-4. Photoluminescence studies showed ligand-sensitized green emissions for 2 with an appreciable quantum yield of 0.83%. Static (dc) and dynamic (ac) magnetic studies of complexes 1 and 3 were performed. The dynamic magnetic study revealed that complex 1 exhibits zero-field slow relaxation of the magnetization without showing a clear maximum in the out-of-phase ac susceptibility plots. However, magnetic dilution of 1 with the YIII metal ion (complex 3) and/or the application of a dc magnetic field induces a strong frequency dependence of the ac susceptibility signals with χ''M peaks in the 3-10 K temperature range, thus supporting field-induced SMM behaviour of 1. The relaxation process takes place through a combination of the Orbach and Raman mechanisms. The fitting of the temperature dependence of the relaxation time to the equation τ-1 = τ0-1 exp(-Ueff/kBT) + BTn, allows the extraction of the effective energy barrier Ueff/kB = 70 K (48.7 cm-1) and pre-exponential parameter of τ0 = 2.7 × 10-7 s for the Orbach mechanism (first term) and the parameters B = 0.04 s-1 K-n and n = 6.11, for the Raman mechanism (second term).
在氢氧化四甲铵存在下，大位阻乙酰丙酮配体1,3 - 二甲基苯甲酰丙酮（MesacacH）与水合镧系氯化物反应，得到了一个新的中性单核LnIII配合物家族[Ln(Mesacac)3(DMF)]（Ln = Dy (1)；Tb (2)；Y0.91Dy0.09 (3)；Er (4)）。通过单晶X射线衍射研究确定了这些配合物的分子结构。通过SHAPE分析对LnIII中心的配位几何结构进行了分析，结果表明1 - 4具有盖帽八面体几何结构。光致发光研究表明，配合物2呈现配体敏化的绿色发射，量子产率可观，为0.83%。对配合物1和3进行了静态（直流）和动态（交流）磁性研究。动态磁性研究表明，配合物1在磁化强度上表现出零场慢弛豫，在异相交流磁化率图中未显示明显的最大值。然而，用YIII金属离子对1进行磁性稀释（配合物3）和/或施加直流磁场会导致交流磁化率信号出现强烈的频率依赖性，在3 - 10 K温度范围内出现χ''M峰，从而支持了1的场诱导单分子磁体行为。弛豫过程通过Orbach和Raman机制的组合发生。将弛豫时间的温度依赖性拟合到方程τ-1 = τ0-1 exp(-Ueff/kBT) + BTn中，可以提取出Orbach机制（第一项）的有效能垒Ueff/kB = 70 K（48.7 cm-1）和预指数参数τ0 = 2.7 × 10-7 s，以及Raman机制（第二项）的参数B = 0.04 s-1 K-n和n = 6.11。
