An Unprecedented Two‐Fold Nested Super‐Polyrotaxane: Sulfate‐Directed Hierarchical Polythreading Assembly of Uranyl Polyrotaxane Moieties

Abstract

The hierarchical assembly of well-organized submoieties could lead to more complicated superstructures with intriguing properties. We describe herein an unprecedented polyrotaxane polythreading framework containing a two-fold nested super-polyrotaxane substructure, which was synthesized through a uranyl-directed hierarchical polythreading assembly of one-dimensional polyrotaxane chains and two-dimensional polyrotaxane networks. This special assembly mode actually affords a new way of supramolecular chemistry instead of covalently linked bulky stoppers to construct stable interlocked rotaxane moieties. An investigation of the synthesis condition shows that sulfate can assume a vital role in mediating the formation of different uranyl species, especially the unique trinuclear uranyl moiety [(UO2 )3 O(OH)2 ](2+) , involving a notable bent [O=U=O] bond with a bond angle of 172.0(9)°. Detailed analysis of the coordination features, the thermal stability as well as a fluorescence, and electrochemical characterization demonstrate that the uniqueness of this super-polyrotaxane structure is mainly closely related to the trinuclear uranyl moiety, which is confirmed by quantum chemical calculations.

Template-Driven Assembly of Rare Hexameric Uranyl-Organic Rotaxane Networks Threaded on Dimeric Uranyl Chains

“…For the MORFs utilizing cucurbituril-based pseudorotaxane/rotaxane linkers, only a handful of MORFs of this type have been reported. , Besides porosity or dynamics for rotaxane-based MOFs, high-order assembly between different well-organized metal–organic rotaxane submoieties and the resulting complicated topology should also be taken into account, as another interesting issue concerning the supramolecular behavior of MORFs is high-order assembly between different well-organized metal–organic rotaxane submoieties just like the assembly of supercoil structure of DNA in biological systems. Whang et al and Liang et al have respectively reported different structural patterns with polycatenating through either inclined interweaving or parallel interpenetration. , In fact, we described another polythreading model of uranyl-containing MORFs, which was based on another assembly mode, that is polythreading . The high-order assembly shown in the above cases verifies the feasibility employing cucurbituril-bearing supramolecular ligands to conduct the high-order assembly of MORFs.…”

“…46,47 In fact, we described another polythreading model of uranyl-containing MORFs, which was based on another assembly mode, that is polythreading. 48 The high-order assembly shown in the above cases verifies the feasibility employing cucurbituril-bearing supramolecular ligands to conduct the high-order assembly of MORFs. Further exploration on new MORFs with high-order assembly will help us to study and understand the supramolecular behavior and weak interactions of pseudorotaxane or rotaxane submoieties during the process of assembly.…”

“…Meanwhile, the dimeric uranyl SBUs also interact with adjacent CB6 molecules of 2D networks through multiple hydrogen bonds . It means that, in order to construct the wide-spreading H-bonds between CB6 (on 1D chains and 2D networks) and uranyl motifs (from hexameric or dimeric units) for the improved stability of polythreading framework structure (Figure and detail H-bond distance are placed in Table S1), the 2D polyrotaxane networks adapted themselves to the shorter sulfate-free chains by narrowing the interlayer distance . In other words, the 1D chains act as template agents, which provide H-bonding sites by CB6 macrocycles and uranyl SBUs to promote not only the formation of 2D networks and final polythreading frameworks, but also the reasonability of uranyl hexameric node.…”

Mixed-Ligand Uranyl Polyrotaxanes Incorporating a Sulfate/Oxalate Coligand: Achieving Structural Diversity via pH-Dependent Competitive Effect

“…To date, there have been numerous reports on the use of MIMs (almost exclusively using pseudorotaxane precursors) as linkers in coordination polymers to create interesting crystalline lattices, ,,− but few of these materials employ actinides as metal nodes. To this end, we have recently reported a series of interesting 1D, 2D, and 3D coordination polymers with rotaxane linkers and uranyl nodes, − which encourage us to pursue more well-designed actinide polyrotaxanes with intriguing topologies and potential functions through the utilization of new synthesis strategies and methods.…”

“…As a new synthesis methodology, a mixed-ligand system provides an alternative route to tune the structure and properties of metal–organic compounds by introducing a second functional organic or inorganic ligand as the coligand. , In our previous work, a similar strategy has been also used to assemble uranyl-organic rotaxane compounds with an inorganic sulfate ion involved. − However, a combination of a pseudorotaxane ligand and simple organic ligands have never been used in uranyl polyrotaxanes. Oxalate, which has been intensively studied for their potential application in actinide separation reprocessing of spent nuclear fuel, could be a versatile ligand with small steric hindrance and different coordination possibilities .…”