National Institute of Materials Physics, R-077125 Magurele, Romania.
J Phys Chem B. 2010 Oct 14;114(40):12840-6. doi: 10.1021/jp1071617.
The molecular mobility of a MOF-5 metal-organic framework was investigated by broadband dielectric spectroscopy. Three relaxation processes were revealed. The temperature dependence of their relaxation rates follows an Arrhenius law. The process observed at lower temperatures is attributed to bending fluctuations of the edges of the cages involving the Zn-O clusters. The processes ("region II") at higher temperatures were assigned to fluctuations of phenyl rings in agreement with the NMR data found by Gould et al. (J. Am. Chem. Soc. 2008, 130, 3246). The carboxylate groups might also be involved. The rotational fluctuations of the phenyl rings leading to the low frequency part of relaxation region II might be hindered either by some solvent molecules entrapped in the cages or by an interpenetrated structure and have a broad distribution of activation energies. The high frequency part of region II corresponds nearly to a Debye-like process: This is explained by a well-defined structure of empty pores.
采用宽频介电谱研究了 MOF-5 金属有机骨架的分子迁移率。揭示了三个弛豫过程。它们的弛豫速率的温度依赖性遵循阿仑尼乌斯定律。在较低温度下观察到的过程归因于包含 Zn-O 簇的笼的边缘的弯曲波动。在较高温度下的过程（“区域 II”）被分配到苯环的波动，与 Gould 等人发现的 NMR 数据一致（J. Am. Chem. Soc. 2008, 130, 3246）。羧酸根也可能参与其中。导致弛豫区域 II 低频部分的苯环的旋转波动可能受到困在笼中的一些溶剂分子或互穿结构的阻碍，并且具有广泛的活化能分布。区域 II 的高频部分几乎对应于德拜型过程：这可以通过空孔的明确定义的结构来解释。
