Controlled Self-Assembly, Isomerism, and Guest Uptake/Release of Charge-Reversible Lanthanide–Organic Octahedral Cages

Abstract

Charge plays a crucial role in the function of molecular and supramolecular systems, but coordination hosts capable of orthogonal charge regulation remain elusive so far. In this study, we report the condition-dependent self-assembly of charge-reversible lanthanide−organic tetra-capped octahedral cages, i.e., [Ln 6 (H 3 L) 4 ] 6+ and [Ln 6 L 4 ] 6− , from a series of lanthanide ions (Ln 3+ ; Ln = Lu, Yb, Eu) and a tritopic tetradentate acylhydrazone ligand (H 6 L) featuring multiple deprotonation states and propeller conformations. While direct self-assembly under basic conditions produced a mixture of various Δ x Λ 6−x -[Ln 6 L 4 ] 6− (x = 0−6) stereoisomers, racemic Δ 6 -and Λ 6 -[Ln 6 L 4 ] 6− could be exclusively obtained from the first self-assembly of Δ 6 -and Λ 6 -[Ln 6 (H 3 L) 4 ] 6+ under neutral conditions followed by postassembly deprotonation. Rich isomerism on the tetra-capped octahedral cages arising from the coupling between the metal-centered Δ/Λ chirality and the ligand conformations has been discussed based on X-ray single-crystal structures of the C 3 -symmetric Δ 3 Λ 3 -Ln 6 L 4 and T-symmetric Δ 6 /Λ 6 -Ln 6 L 4 complexes. Host−guest studies confirmed that positively charged rac-Δ 6 /Λ 6 -[Ln 6 (H 3 L) 4 ] 6+ could bind anionic sulfonates, and negatively charged rac-Δ 6 /Λ 6 -[Ln 6 L 4 ] 6− exhibited strong encapsulation ability toward ammonium guests, where acid/base-triggered guest uptake/release could be realized taking advantage of the charge reversibility of the cage. Moreover, photophysical studies revealed visible-light-sensitized and guest-encapsulation-enhanced NIR emissions on the rac-Δ 6 / Λ 6 -Yb 6 L 4 cage. This work not only enriches the library of functional lanthanide−organic cages but also provides a promising candidate with charge reversibility for the development of smart supramolecular materials.

Magnetic and Porous Regulation in Cobalt(II) Hydrogen-Bonded Organic Framework via Supramolecular Isomerism

“…These isomers serve as intriguing molecular systems for studying structure–property relationships and unveiling the self-assembly processes of supramolecular materials. , This intriguing phenomenon has garnered widespread attention. To date, various types of isomerism, such as supramolecular isomerism, interpenetration isomerism, , and topological isomerism, have been observed in different types of crystalline porous materials. However, although a variety of MOF isomers have been reported, supramolecular framework isomers originating from distinct supramolecular interactions, such as HOF isomers, are extremely rare.…”

Cage‐To‐Cage Transformations in Self‐Assembled Coordination Cages Using “Acid/Base” or “Guest Binding‐Induced Strain” as Stimuli

“…[11][12][13][14][15][16] Different design strategies were employed to subtly alter the guest binding capabilities of coordination cages that include post-assembly modification using stimuli. [17][18][19][20] Stimuli-responsive behavior in combination with labile coordination bonds have afforded captivating structural transformations in coordination cages, with/without the change in chemical composition of the cages, in response to stimuli. [20][21][22][23][24][25] M 2 L 4 -type cages are one of the well-known architectural entities (majority are Pd 2 L 4 type) which, upon suitable design, can respond to various stimuli like pH, redox, chemical and light.…”

A CuI6L4 Cage Dynamically Reconfigures to Form Suit[4]anes and Selectively Bind Fluorinated Steroids

“…21 The dynamic nature of metal−organic coordination cages can allow their transformation in response to stimuli, 22 including light, 23,24 concentration, 25,26 temperature, 27 guest presence, 28−30 and solvent. 31,32 However, fewer cages have been reported to respond to combinations of these stimuli. 33 The novel class of suit[n]anes, introduced by Stoddart's group, 34 are a class of interlocked supramolecular assemblies where multiple arms of a guest protrude through the apertures of a polycyclic host, resulting in mechanical bonding 35−37 between guest and host.…”

“…The 1 H DOSY NMR spectra of G2⊂T-1 and G3⊂T-1 (Figures S55 and S69) showed all signals corresponding to host and guest diffusing together, with solvodynamic radii of 13.2 and 12.3 Å, In G3⊂T-1, each of the biphenyl arms of G3 protrudes through the center of a triangular pore, forming an interlocked suit [4]ane. 38 Although tetrahedral guest molecules have previously been encapsulated within the cavities of cages, 32 to the best of our knowledge G3⊂T-1 is the first example of a suit[n]ane with a three-dimensional central axle component protruding through a nonplanar array of pores in a mechanically bonded configuration. 38 Its structure thus builds upon those of previously reported suit[n]anes, which have rigid planar axles protruding through coplanar macrocyclic pores.…”

“…Whereas metal ions with square-planar , and octahedral , coordination geometries are widely used in metal–organic cages, tetrahedral copper­(I) has seen less use. , Although Cu I –imine mononuclear complexes , and helicates , have been reported, fewer examples of Cu I –imine coordination cages with internal cavities have been reported . The dynamic nature of metal–organic coordination cages can allow their transformation in response to stimuli, including light, , concentration, , temperature, guest presence, − and solvent. , However, fewer cages have been reported to respond to combinations of these stimuli …”