Copper-Linked Rotaxanes for the Building of Photoresponsive Metal Organic Frameworks with Controlled Cargo Delivery

Abstract

We have prepared a photoresponsive metal–organic framework by using an amide-based [2]­rotaxane as linker and copper­(II) ions as metal nodes. The interlocked linker was obtained by the hydrogen bond-directed approach employing a fumaramide thread as template of the macrocyclic component, this latter incorporating two carboxyl groups. Single crystal X-ray diffraction analysis of the metal–organic framework, prepared under solvothermal conditions, showed the formation of stacked 2D rhombohedral grids forming channels decorated with the interlocked alkenyl threads. A series of metal–organic frameworks differing in the E/Z olefin ratio were prepared either by the previous isomerization of the linker or by postirradiation of the reticulated materials. By dynamic solid state 2H NMR measurements, using deuterium-labeled materials, we proved that the geometry of the olefinic axis of the interlocked struts determined the obtention of materials with different independent local dynamics as a result of the strength of the intercomponent noncovalent interactions. Moreover, the usefulness of these novel copper-rotaxane materials as molecular dosing containers has also been assayed by the diffusion and photorelease of p-benzoquinone, evaluated in different solvents and temperatures.

Effective Encapsulation of C60 by Metal–Organic Frameworks with Polyamide Macrocyclic Linkers

“…In those materials the presence of an interlocked thread inside the macrocyclic cavity precluded the formation of 1D polymers such as in 5 a . The absence of the thread in the novel UMUMOF 5 a is shown to cause an increase in flexibility and a larger pore size, probably due to the larger conformational space of the non‐interlocked macrocyclic ligand and the lesser steric demand in comparison to that of a rotaxane [24, 33] having the same macrocycle.…”

“…The dimension of the channel created between two copper clusters and two macrocycles is defined by the distance between the Cu II paddlewheels (19.47 Å) and the distance of the centroids of the p ‐xylylene rings of each macrocycle (10.96 Å). Interestingly, we have previously reported the building of 2D‐periodic Cu‐based metal–organic frameworks by using rotaxane ligands bearing similar tetralactam macrocycles [24] . In those materials the presence of an interlocked thread inside the macrocyclic cavity precluded the formation of 1D polymers such as in 5 a .…”

Effective Encapsulation of C60 by Metal–Organic Frameworks with Polyamide Macrocyclic Linkers

“…Herein, we describe the building of copper(II)‐ and zinc (II)‐organic frameworks that incorporate a benzylic amide macrocycle bearing two carboxylic acid linkers as a ditopic ligand. We have previously reported the preparation of metal–organic frameworks by using similar but interlocked macrocycles in the form of [2]rotaxanes [24] . Thus, the results of the present work will allow to compare how the absence or presence of the mechanical bond affects the molecular arrangement of nearly identical constituents (macrocycle vs. rotaxane) in the crystalline network.…”

Temperature‐Triggered Structural Dynamics of Non‐Coordinating Guest Moieties in a Fluorescent Actinide Polyrotaxane Framework

“…Dynamic motions are hard to achieve in these compounds, because of their intrinsic tightly‐packing structures derived from the interlocked features of the pseudorotaxane precursors. Type C is much more rarely observed, and has only been reported recently in MORFs based on MIMs with functionalized macrocycles including pillararene [6] and cycloaramide [7] . Unlike the string molecules in type A or B tightly fixed with the secondary building units (SBUs) consisting of different metal cations, the string components of type C may show more flexibility.…”