Rotating Phenyl Rings as a Guest-Dependent Switch in Two-Dimensional Metal–Organic Frameworks

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• 作者：Christopher R. Murdock ; Nicholas W. McNutt ; David J. Keffer ; David M. Jenkins
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：January 15, 2014
• 年：2014
• 卷：136
• 期：2
• 页码：671-678
• 全文大小：530K
• ISSN：1520-5126

文摘

A semirigid bis(1,2,4-triazole) ligand binds in a syn conformation between copper(I) chains to form a series of two-dimensional metal鈥搊rganic frameworks that display a topology of fused one-dimensional metal鈥搊rganic nanotubes. These anisotropic frameworks undergo two different transformations in the solid state as a function of solvation. The 2D sheet layers can expand or contract, or, more remarkably, the phenyl rings can rotate between two distinct positions. Rotation of the phenyl rings allows for the adjustment of the tube size, depending on the guest molecules present. This 鈥済ate鈥?effect along the 1D tubes has been characterized through single-crystal X-ray diffraction. The transformations can also be followed by powder X-ray diffraction (PXRD) and solid-state ¹³C cross-polarization magic-angle-spinning (CP-MAS) NMR. Whereas PXRD cannot differentiate between transformations, solid-state ¹³C CP-MAS NMR can be employed to directly monitor phenyl rotation as a function of solvation, suggesting that this spectroscopic method is a powerful approach for monitoring breathing in this novel class of frameworks. Finally, simulations show that rotation of the phenyl ring from a parallel orientation to a perpendicular orientation occurs at the cost of framework鈥揻ramework energy and that this energetic cost is offset by stronger framework鈥搒olvent interactions.