Capsule Formation, Carboxylate Exchange, and DFT Exploration of Cadmium Cluster Metallocavitands: Highly Dynamic Supramolecules

Noncooperative guest binding by metal-free [2 + 2] Schiff-base macrocycles

Salphen-based [n + n] macrocycles have been widely explored for their unique chemical and topological properties following metal ion coordination. Despite having vastly different reactivity than their coordinated counterparts, fewer studies have focused on metal-free salphen macrocycles. We investigated the binding of [2 + 2] Schiff-base macrocycle host 3, which contains a central 18-crown-6-like cavity and two N₂O₂ moieties. This macrocycle strongly binds to spherical cationic guests (K₁₁ ≈ 10³-10⁴ M^-1, DCM/MeCN). The most robust binding was shown for K⁺ and Na⁺, followed by Li⁺ and Rb⁺. More sterically demanding cationic guests like dibenzylammonium (DBA⁺) showed almost no binding. The binding pocket in 3 is slightly smaller than 18-crown-6, resulting in binding outside the cavity, which provides a scaffold appropriate for 2 : 1 complexes, where two host molecules sandwich the guest. All host-guest complexes follow a 2 : 1 noncooperative binding model, where each successive binding event is less likely than the previous, unlike coordinated versions of 3, where most binding is 1 : 1.

Contemporary macrocycles for discrete polymetallic complexes: precise control over structure and function

The growth of multimetallic clusters and complexes can proceed in the presence of suitable ligands, but often leads to polydisperse structures with poor solubility. As an alternative approach, macrocyclic molecules can anchor the multimetallic complex, directing its formation and stabilizing the resulting product. This approach can provide excellent control over the growth of clusters, and offers a handle to control solubility and other properties of the resulting complexes. In this Tutorial Review, we discuss recent activity (primarily the last two decades) directed at the controlled and reproducible synthesis of multimetallic complexes using macrocyclic ligands. Throughout the review, we focus on the unusual structures that are only accessible by using macrocycles as ligands, and their unique properties.

Diverse binding of cationic guests by highly substituted [3 + 3] Schiff-base macrocycles

Schiff-base macrocycles interact with ammonium-based guests to form threaded pseudorotaxanes or unthreaded external complexes, and tautomerize in the process.

Recent advances in solid-state nuclear magnetic resonance spectroscopy of exotic nuclei

We present a review of recent advances in solid-state nuclear magnetic resonance (SSNMR) studies of exotic nuclei. Exotic nuclei may be spin-1/2 or quadrupolar, and typically have low gyromagnetic ratios, low natural abundances, large quadrupole moments (when I > 1/2), or some combination of these properties, generally resulting in low receptivities and/or prohibitively broad line widths. Some nuclides are little studied for other reasons, also rendering them somewhat exotic. We first discuss some of the recent progress in pulse sequences and hardware development which continues to enable researchers to study new kinds of materials as well as previously unfeasible nuclei. This is followed by a survey of applications to a wide range of exotic nuclei (including e.g., ⁹Be, ²⁵Mg, ³³S, ³⁹K, ⁴³Ca, ^47/49Ti, ⁵³Cr, ⁵⁹Co, ⁶¹Ni, ⁶⁷Zn, ⁷³Ge, ⁷⁵As, ⁸⁷Sr, ¹¹⁵In, ¹¹⁹Sn, ^121/123Sb, ^135/137Ba, ^185/187Re, ²⁰⁹Bi), most of them quadrupolar. The scope of the review is the past ten years, i.e., 2007-2017.

Expanded campestarene hosts for tetra- and dinuclear uranyl(vi) complexes

Expanded campestarene macrocycles with keto–enamine structures host dinuclear and tetranuclear hydroxo-bridged uranyl(vi) clusters in their interiors.

Cage-like crystal packing through metallocavitands within a cobalt cluster-based supramolecular assembly

The generation of cage-like crystal packing geometry of TSHs in the solid state induced by the host–guest interactions among metallocavitands.

The role of solid-state nuclear magnetic resonance in crystal engineering

This Highlight article discusses the role of solid-state NMR spectroscopy in crystal engineering with the aid of several examples from the literature.

Extremely strong tubular stacking of aromatic oligoamide macrocycles

As the third-generation rigid macrocycles evolved from progenitor 1, cyclic aromatic oligoamides 3, with a backbone of reduced constraint, exhibit extremely strong stacking with an astoundingly high affinity (estimated lower limit of Kdimer > 1013 M-1 in CHCl3), which leads to dispersed tubular stacks that undergo further assembly in solution. Computational study reveals a very large binding energy (-49.77 kcal mol-1) and indicates highly cooperative local dipole interactions that account for the observed strength and directionality for the stacking of 3. In the solid-state, X-ray diffraction (XRD) confirms that the aggregation of 3 results in well-aligned tubular stacks. The persistent tubular assemblies of 3, with their non-deformable sub-nm pore, are expected to possess many interesting functions. One such function, transmembrane ion transport, is observed for 3.

Lyotropic liquid crystallinity in mixed-tautomer Schiff-base macrocycles

New Schiff-base macrocycles that combine keto-enamine and enol-imine tautomers are reported. As well as forming host–guest complexes with organic cations, these macrocycles form a lyotropic liquid crystal in organic solvents.

Bulky metallocavitands with a chiral cavity constructed by aluminum and magnesium atrane-likes: enantioselective recognition and separation of racemic alcohols

Novel tetranuclear metallocavitands with a chiral cavity were synthesized via self-assembly of aluminum/magnesium atrane-likes and were successfully applied to the chiral resolution of 2-butanol.

Giant electroactive M4L6 tetrahedral host self-assembled with Fe(II) vertices and perylene bisimide dye edges

Self-assembly of octahedral Fe(II) ions and linear perylene bisimide (PBI) dyes with 2,2'-bipyridine groups covalently attached at the imide positions quantitatively yields an Fe4(PBI)6 tetrahedron by the directional bonding approach. With an edge length of 3.9 nm and estimated internal volume >950 Å(3), tetrahedron T is one of the largest M4L6 tetrahedra ever reported. Importantly, many of the desirable photo- and electroactive properties of the PBI ligands are transferred to the nanoscale metallosupramolecule. Tetrahedron T absorbs strongly across the visible spectrum out to 650 nm and exhibits a total of 7 highly reversible electrochemical oxidation and reduction waves spanning a 3.0 V range. This facile cycling of 34 electrons between +18 and -16 charged species is likely enabled due to the porous nature of the tetrahedron that allows the necessary counterions to freely flow in and out of the host. Host-guest encapsulation of C60 by T in acetonitrile was studied by (13)C NMR spectroscopy, UV-vis spectroscopy, and ESI-MS, confirming that the tetrahedron is a suitable host for large, functional guest molecules.

Metals, macrocycles and molecular assemblies - macrocyclic complexes in metallo-supramolecular chemistry

In this tutorial review the use of macrocyclic complexes as building blocks in a selection of supramolecular systems is discussed with emphasis on the properties, such as enhanced stabilities, that cyclic ligands and their complexes may impart on the resulting assemblies. An aim of the review is to exemplify the versatility of macrocyclic ligand complexes for use as components in a range of both discrete and polymeric systems. The use of macrocyclic systems for controlling CuI aggregation, as scaffolds for metal-cluster formation, as the cyclic components in interlocked catenane and rotaxane structures, for constructing assemblies based on macrocycle exo-coordination, for forming columnar stacks, as well as their roles as both structural and redox centres in a range of coordination polymer types are all presented.