Highly branched and loop-rich gels via formation of metal–organic cages linked by polymers

Abstract

Gels formed via metal–ligand coordination typically have very low branch functionality, f, as they consist of ∼2–3 polymer chains linked to single metal ions that serve as junctions. Thus, these materials are very soft and unable to withstand network defects such as dangling ends and loops. We report here a new class of gels assembled from polymeric ligands and metal-organic cages (MOCs) as junctions. The resulting ‘polyMOC’ gels are precisely tunable and may feature increased branch functionality. We show two examples of such polyMOCs: a gel with a low f based on a M2L4 paddlewheel cluster junction and a compositionally isomeric one of higher f based on a M12L24 cage. The latter features large shear moduli, but also a very large number of elastically inactive loop defects that we subsequently exchanged for functional ligands, with no impact on the gel's shear modulus. Such a ligand substitution is not possible in gels of low f, including the M2L4-based polyMOC.

Discrete and Polymeric Self‐Assembled Palladium(II) Complexes as Supramolecular Gelators

“…[27][28][29][30][31][32][33][34][35][37][38][39][40] Te ntative compositions for polymeric gelators peciesa re proposed in some cases;f or other cases we have proposed indicative compositions that are, however,h ypothetical. [27][28][29][30][31][32][33][34][35][37][38][39][40] Te ntative compositions for polymeric gelators peciesa re proposed in some cases;f or other cases we have proposed indicative compositions that are, however,h ypothetical.…”

“…[33] TEM analysis of metallogel 22' confirmed the presence of af ibrous network structure with af iber diameter of about 70 to 120 nm (Figure 22b) Xu and co-workers also prepared self-assembled samples in DMSO by combining cis-[Pd(en)(NO 3 ) 2 ]w ith porphyrin-based tetrapyridyl ligand L23 in one case and Pd(OAc) 2 with tripodal ligand L23 in another case. [34] Polymeric palladium(II) complexes of tetradentate ligands with polymeric spacers as metallogelators Johnson and co-workers introduced an ew class of polymerbased metallogels ( Figure 25) [35] that are very different from conventional supramolecular metallogels. [33] TEM images confirmed the presence of nanofibers ( Figures 23b and 24b).…”

“…Miravet and Escuder used an organic gel as as upport and immobilizedp alladium(II) in the organogel matrix. [35] The proposal of the junction was made on the basis of the complexation of L26' with Pd(NO 3 ) 2 ,w hich resulted in the formation of a[ Pd 2 L 4 ]-type binuclear complex, [Pd 2 (L26') 4 ] n (NO 3 ) 4n (26'). [34] Polymeric palladium(II) complexes of tetradentate ligands with polymeric spacers as metallogelators Johnson and co-workers introduced an ew class of polymerbased metallogels ( Figure 25) [35] that are very different from conventional supramolecular metallogels.…”

Star PolyMOCs with Diverse Structures, Dynamics, and Functions by Three‐Component Assembly

“…[23][24][25][26][27][28][29] Inspired by this structural versatility and potential applications such as mechanical enhancement, catalysis, encapsulation, sensing, etc., much effort has been recently devoted to installing MOCs into polymer networks to provide 'polyMOC' hybrid materials with tunable viscoelasticity and functionality. [30][31][32][33][34][35][36][37] One [30,[38][39][40][41][42] ; however, there is still a great need to understand how polyMOC microstructure translates to bulk material properties such as modulus and relaxation dynamics. To accomplish this goal, robust, modular polyMOC synthesis strategies that enable access to a wide range of structures and properties are needed.…”

“…[31] Nitschke and co-workers reported hydrogel polyMOCs crosslinked by tetrahedral MOCs that could selectively encapsulate and release small molecules. [32] Several other recent examples of MOCcontaining polymeric materials highlight the potential of these systems [30,[38][39][40][41][42] ; however, there is still a great need to understand how polyMOC microstructure translates to bulk material properties such as modulus and relaxation dynamics.…”