Mechanically Interlocked Linkers inside Metal–Organic Frameworks: Effect of Ring Size on Rotational Dynamics

A series of metal–organic framework (MOF) materials has been prepared, each containing a mechanically interlocked molecule (MIM) as the linker and a copper­(II) paddlewheel as the secondary building unit (SBU). The MIM linkers are [2]­rotaxanes with varying sizes of crown ether macrocycles ([22]­crown-6, 22C6; [24]­crown-6, 24C6; [26]­crown-6, 26C6; benzo[24]­crown-6, B24C6) and an anilinium-based axle containing four carboxylate donor groups. Herein, the X-ray structures of MOFs UWCM-1 (no crown) and UWDM-1₍₂₂₎ are compared and demonstrate the effect of including a macrocycle around the axle of the linker. The rotaxane linkers are linear and result in nbo-type MOFs with void space that allows for motion of the interlocked macrocycle inside the MOF pores, while the macrocycle-free linker is bent and yields a MOF with a novel 12-connected bcc structure. Variable temperature ²H solid-state nuclear magnetic resonance showed that the macrocycles in UWDM-1₍₂₂₎, UWDM-1₍₂₄₎, and UWDM-1_(B24) undergo different degrees and rates of rotation depending on the size and shape of the macrocycle.