Framework mobility in the metal-organic framework crystal IRMOF-3: Evidence for aromatic ring and amine rotation
Framework mobility in the metal-organic framework crystal IRMOF-3: Evidence for aromatic ring and amine rotation
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DOI：
10.1016/j.molstruc.2011.07.037
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发表时间：
2011-10-12
影响因子：
3.8
通讯作者：
Garcia-Garibay, Miguel A.
中科院分区：
文献类型：
--
作者：
Morris, William;Taylor, R. E.;Garcia-Garibay, Miguel A.
用H-1核磁共振弛豫方法研究了IRMOF-3(BDC-NH_2代表2-氨基-1，4-苯二甲酸根)中的骨架运动。N-15对2-氨基的同位素浓缩对于阐明晶格动力学和提高光谱分辨率是至关重要的。结果表明，BDC-NH_2中氨基的转动是一个低能过程，活化能为1.8+/-0.6kcal/mol，苯基的转动为180度，活化能为5.0+/-0.2kcal/mol。胺旋转的指数前因子相对较低(1.3x10(7)S(-1))，初步认为需要打破氢键作为速率限制步骤。胺的旋转和芳环的翻转都发生在为氨基中99.6%的天然丰度的四极N-14提供有效驰豫机制的频率。N-14与相邻的自旋1/2核(H-1和C-13)的偶极耦合不仅在静态样品中发生，而且在本研究使用的7T磁场下的MAS实验中也发生。结果，自旋动力学和交叉极化动力学受到影响，导致光谱展宽。在MAS实验中，用N-15取代自然丰度N-14显著提高了N-15光谱以及H-1和C-13光谱的分辨率。(C)2011爱思唯尔B.V.保留所有权利。
The framework motions in IRMOF-3 (Zn4O(BDC-NH2)(3)), where BDC-NH2 represents 2-amino-1,4-ben zenedicarboxylate, have been investigated with H-1 NMR relaxation measurements. Isotopic enrichment of the 2-amino group with N-15 was critical in elucidating the lattice dynamics and enhancing spectral resolution. These results indicate a low energy process associated with rotation of the amino group, with an activation energy of 1.8 +/- 0.6 kcal/mol, and full 180 rotation of the phenylene group in the BDC-NH2 moiety with an activation energy of 5.0 +/- 0.2 kcal/mol. A relatively low pre-exponential factor for amine rotation (1.3 x 10(7) s(-1)) is tentatively associated with the need to break a hydrogen bond as the rate-limiting step. Both amine rotation and the aromatic ring flip occur at frequencies that provide an effective relaxation mechanism for the 99.6% natural abundance quadrupolar N-14 in the amino group. Dipolar coupling of the N-14 to adjacent spin-1/2 nuclei (both H-1 and C-13) occurs not only in the static sample but also in the MAS experiments at the 7 T magnetic field used in this study. As a result, the spin dynamics and the cross-polarization dynamics are affected, resulting in spectral broadening. In the MAS experiments, isotopic replacement of the natural abundance N-14 with N-15 significantly improves resolution of the N-15 spectra as well as in the H-1 and C-13 spectra. (C) 2011 Elsevier B.V. All rights reserved.