Metal鈥揙rganic Frameworks with Mechanically Interlocked Pillars: Controlling Ring Dynamics in the Solid-State via a Reversible Phase Change

详细信息    查看全文

• 作者：Kelong Zhu ; V. Nicholas Vukotic ; Christopher A. O鈥橩eefe ; Robert W. Schurko ; Stephen J. Loeb
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：May 21, 2014
• 年：2014
• 卷：136
• 期：20
• 页码：7403-7409
• 全文大小：510K
• 年卷期：v.136,no.20(May 21, 2014)
• ISSN：1520-5126

文摘

Metal鈥搊rganic framework (MOF) materials have been prepared that contain a mechanically interlocked molecule (MIM) as the pillaring strut between two periodic Zn-carboxylate layers. The MIM linker is a [2]rotaxane with a [24]crown-6 (24C6) macrocycle and an aniline-based axle with terminal pyridine donor groups. The single-crystal X-ray structures of MOFs UWDM-2 (1,4-diazophenyl-dicarboxylate) and UWDM-3 (1,4-biphenyl-dicarboxylate) show that both frameworks are large enough to contain the free volume required for rotation of the interlocked 24C6 macrocycle, but the frameworks are interpenetrated (UWDM-2, three-fold, and UWDM-3, two-fold). In particular, for UWDM-3 the 24C6 rings of the pillaring MIM are positioned directly inside the square openings of neighboring zinc dicarboxylate layers. Variable-temperature (VT) ²H SSNMR demonstrated that the 24C6 macrocycles in UWDM-2 and UWDM-3 can only undergo restricted motions related to ring flexibility or partial rotation but are incapable of undergoing free rotation. VT-powder X-ray diffraction studies showed that upon activation of UWDM-3, by removing solvent, a phase change occurs. The new 尾-phase of UWDM-3 retained crystallinity, and ²H SSNMR demonstrated that the 24C6 macrocyclic ring of the pillared MIM strut is now free enough to undergo full rotation. Most importantly, the phase change is reversible; the 尾 version of the MOF can be reverted to the original 伪 state by resolvation, thus demonstrating, for the first time, that the dynamics of a MIM inside a solid material can be controlled by a reversible phase change.