Lanthanide-Based Porous Coordination Polymers: Syntheses, Slow Relaxation of Magnetization, and Magnetocaloric Effect
Lanthanide-Based Porous Coordination Polymers: Syntheses, Slow Relaxation of Magnetization, and Magnetocaloric Effect
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DOI：
10.1021/acs.inorgchem.8b00720
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发表时间：
2018-06-04
影响因子：
4.6
通讯作者：
Shanmugam, Maheswaran
中科院分区：
文献类型：
--
作者：
Das, Chinmoy;Upadhyay, Apoorya;Shanmugam, Maheswaran
分离出两种结构相似的含镧系多孔配位聚合物（pcp），分子式为[Ln(2)(L-1)(2)(H2O)(4)(ox)(n)]。4nH(2)O(其中L-1 =富马酸盐，ox =草酸盐；Ln = Dy （1), Gd(2)）。热重分析（TGA）和热质谱分析（TG-MS）表明，在激活后，不仅晶格中的溶剂化水分子被去除，而且1和2中各自镧系元素上的四个配位水分子也被去除。通过粉末x射线衍射（PXRD）证实，由于水的去除，1和2失去了结晶度，变成了无定形。基于XANES， EXAFS和其他实验研究，我们提出了1和2的非晶态相(Ln = Dy （1'), Gd(2')）的分子式[Ln(2)(L-1)(2)(ox)](n)。研究了1和1′的磁化弛豫动力学，揭示了1′的有效能垒分别为53.5和7.0 cm(-1)， 1′的有效能垒分别为45.1和6.4 crn（-1）的两种不同的弛豫过程，并通过详细的从头计算进行了合理化。对于各向同性镧系配合物2和2′，通过详细的磁化测量估计了磁热效应（MCE）效率。我们估计2‘和2’的- delta S-m值分别为52.48和41.62 J kg(1-)K(-1)，这是对扩展结构报道的最大值之一。此外，通过简单地去除晶格中被动贡献（对于MCE）的溶剂化水分子和配位水分子，与2相比，2'中的- δ S-m值增加了26%。
Two lanthanide-containing structurally analogous porous coordination polymers (PCPs) have been isolated with the general molecular formula [Ln(2)(L-1)(2)(H2O)(4)(ox)(n).4nH(2)O (where L-1 = fumarate, ox = oxalate; Ln = Dy (1), Gd (2)). Thermogravimetric analysis (TGA) and TG-MS measurements performed on 1 and 2 suggest that not only the solvated water molecules in the crystal lattice but also the four coordinated water molecules on the respective lanthanides in 1 and 2 are removed upon activation. Due to the removal of the waters, 1 and 2 lost their crystallinity and became amorphous, as confirmed by powder X-ray diffraction (PXRD). We propose the molecular formula [Ln(2)(L-1)(2)(ox)](n) for the amorphous phase of 1 and 2 (where Ln = Dy (1'), Gd (2')) on the basis of XANES, EXAFS, and other experimental investigations. Magnetization relaxation dynamics probed on 1 and 1' reveal two different relaxation processes with effective energy barriers of 53.5 and 7.0 cm(-1) for 1 and 45.1 and 6.4 crn(-1) for 1', which have been rationalized by detailed ab initio calculations. For the isotropic lanthanide complexes 2 and 2', magnetocaloric effect (MCE) efficiency was estimated through detailed magnetization measurements. We have estimated -Delta S-m values of 52.48 and 41.62 J kg(1-)K(-1) for 2' and 2, respectively, which are one of the largest values reported for an extended structure. In addition, a 26% increase in -Delta S-m value in 2' in comparison to 2 is achieved by simply removing the passively contributing (for MCE) solvated water molecule in the lattice and coordinated water molecules.