Stacked Platinum Complexes of the Magnus’ Salt Type Inside a Coordination Cage

Hexaphenyltriphenylene-Based Multicomponent Metallacages: Host-Guest Complexation for White-Light Emission

A hexaphenyltriphenylene-based hexatopic pyridyl ligand is designed and used to prepare three hexagonal prismatic metallacages via metal-coordination-driven self-assembly. Owing to the planar conjugated structures of the hexaphenyltriphenylene skeleton, such metallacages show good host-guest complexation with a series of emissive dyes, which have been further used to tune their emission in solution. Interestingly, based on their complementary emission colors, white light emission is achieved in a mixture of the host metallacages and the guests.

Hexaphenylbenzene-Based Deep Blue-Emissive Metallacages as Donors for Light-Harvesting Systems

We herein report the preparation of a series of hexaphenylbenzene (HPB)-based deep blue-emissive metallacages via multicomponent coordination-driven self-assembly. These metallacages feature prismatic structures with HPB derivatives as the faces and tetracarboxylic ligands as the pillars, as evidenced by NMR, mass spectrometry and X-ray diffraction analysis. Light-harvesting systems were further constructed by employing the metallacages as the donor and a naphthalimide derivative (NAP) as the acceptor, owing to their good spectral overlap. The judiciously chosen metallacage serves as the antenna, providing the suitable energy to excite the non-emissive NAP, and thus resulting in bright emission for NAP in the solid state. This study provides a type of HPB-based multicomponent emissive metallacage and explores their applications as energy donors to light up non-emissive fluorophores in the solid state, which will advance the development of emissive metallacages as useful luminescent materials.

Coordination Self-Assembly Processes Revealed by Collaboration of Experiment and Theory: Toward Kinetic Control of Molecular Self-Assembly

The importance of the collaboration of experiment and theory has been proven in many examples in science and technology. Here, such a new example is shown in the investigation of molecular self-assembly process, which is a complicated multi-step chemical reaction occurring in the reaction network composed of a huge number of intermediates. An experimental method, QASAP (quantitative analysis of self-assembly process), developed by us and a numerical approach, NASAP (numerical analysis of self-assembly process), that analyzes the experimental data obtained by QASAP to draw detail molecular self-assembly pathways, which was also developed by us, are introduced, and their application to the investigation of Pd(II)-mediated coordination assemblies are presented. Further, the possibility of the prediction of the outcomes of molecular self-assembly by varying the reaction conditions is also demonstrated. Finally, a future direction in the field of artificial molecular self-assembly based on pathway-dependent self-assembly, that is, kinetic control of molecular self-assembly is discussed.

Hierarchical Frameworks of Metal-Organic Cages with Axial Ferroelectric Anisotropy

Designing molecular crystals with switchable dipoles for ferroelectric applications is challenging and often serendipitous. Herein, we show a systematic approach toward hierarchical 1D, 2D and 3D frameworks that are assembled through successive linkage of metal-organic cages [Cu₆ (H₂ O)₁₂ (TPTA)₈ ]¹²⁺ with chloride ions. Their ferroelectric properties are due to the displacement of channel-bound nitrate counterions and solvated water molecules relative to the framework of cages. Ferroelectric measurements of crystals of discrete and 1D-framework assemblies showed axial ferroelectric anisotropy with high remnant polarisation. Both, the reversible formation of cage-connected networks and the observation of ferroelectric anisotropic behaviour are rare among metal-ligand cage assemblies.

Quantitative Analysis of Self-Assembly Process of a Pd2 L4 Cage Consisting of Rigid Ditopic Ligands

The self-assembly process of a Pd₂ L₄ cage complex consisting of rigid ditopic ligands, in which two 3-pyridyl groups are connected to a benzene ring through acetylene bonds and Pd^II ions was revealed by a recently developed quantitative analysis of self-assembly process (QASAP), with which the self-assembly process of coordination assemblies can be investigated by monitoring the evolution with time of the average composition of all the intermediates. QASAP revealed that the rate-determining steps of the cage formation are the intramolecular ligand exchanges in the final stage of the self-assembly: [Pd₂ L₄ Py*₂ ]⁴⁺ →[Pd₂ L₄ Py*₁ ]⁴⁺ +Py* and [Pd₂ L₄ Py*₁ ]⁴⁺ →[Pd₂ L₄ ]⁴⁺ +Py* (Py*: 3-chloropyridine, which was used as a leaving ligand on the metal source). The energy barriers for the two reactions were determined to be 22.3 and 21.9 kcal mol^-1 , respectively. DFT calculations of the transition-state (TS) structures for the two steps indicated that the distortion of the trigonal-bipyramidal Pd^II center at the TS geometries increases the activation free energy of the two steps.

Multicavity Metallosupramolecular Architectures

Discrete metallosupramolecular systems are often macrocyclic or cage-like architectures with an accessible internal cavity. Guest molecules can reside within these cavities and much of the interest in these systems is derived from these fascinating host-guest interactions. A range of potential applications stem from the ability of these metallosupramolecular architectures to encapsulate guests. These applications include catalysis or acting as molecular reaction flasks, the molecular scavenging of pollutants, storage of reactive species, and drug delivery. Multicavity metallosupramolecular architectures combine the ability of large hollow assemblies to bind multiple guests concurrently with the binding specificity associated with small cages. A variety of different approaches to generating separate compartments within a single metallosupramolecular assembly have emerged. These include interpenetrated cages, cages with polytopic ligands that have a long backbone, and molecules that have two or more clefts. This review examines these approaches, and highlights key contributions to the field.

Modular synthesis of linear bis- and tris-monodentate fused [6]polynorbornane-based ligands and their assembly into coordination cages

A modular approach has been developed for the synthesis of rigid linear di- and tritopic ligands based on a fused [6]polynorbornane scaffold. The design provides up to three sites for installing functionality, including both "ends" and a "central" position with the advantage that each region can be independently addressed during synthesis. To illustrate the utility of the approach, both pyridyl and picolyl units were incorporated to provide six new ligands, with centers and ends either matched or mismatched. Indeed, both [M2L4] cages with endohedral functionality and [M3L4] complexes were cleanly produced from these ligands with assembled structures confirmed by using (1)H NMR spectroscopy, HRMS, and molecular modelling.

Stoichiometrically controlled revocable self-assembled "spiro" versus quadruple-stranded "double-decker" type coordination cages

The simple combination of Pd(II) with the tris-monodentate ligand bis(pyridin-3-ylmethyl) pyridine-3,5-dicarboxylate, L, at ratios of 1:2 and 3:4 demonstrated the stoichiometrically controlled exclusive formation of the "spiro-type" Pd1L2 macrocycle, 1, and the quadruple-stranded Pd3L4 cage, 2, respectively. The architecture of 2 is elaborated with two compartments that can accommodate two units of fluoride, chloride, or bromide ions, one in each of the enclosures. However, the entry of iodide is altogether restricted. Complexes 1 and 2 are interconvertible under suitable conditions.

A new structural motif for an enantiomerically pure metallosupramolecular Pd₄L₈ aggregate by anion templating

An enantiomerically pure BINOL-based bis(3-pyridyl) ligand 1 assembles into a homochiral [Pd4(1)8] complex upon coordination to tetravalent Pd(II) ions. The formation of this aggregate is templated by two tetrafluoroborate counterions that are encapsulated in two peripheral cavities. The resulting structure is a new structural motif for this kind of metallosupramolecular assemblies that arranges the palladium ions in a distorted tetrahedral fashion and forces ligand 1 to adopt two different conformations. Both phenomena are unique and cause an overall three-dimensional structure that has another confined, chiral, and hydrophilic central cavity.

Self-assembled tetragonal prismatic molecular cage highly selective for anionic π guests

The metal-directed supramolecular synthetic approach has paved the way for the development of functional nanosized molecules. In this work, we report the preparation of the new nanocapsule 3·(CF(3)SO(3))(8) with a A(4 B(2) tetragonal prismatic geometry, where A corresponds to the dipalladium hexaazamacrocyclic complex Pd-1, and B corresponds to the tetraanionic form of palladium 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin (2). The large void space of the inner cavity and the supramolecular affinity for guest molecules towards porphyrin-based hosts converts this nanoscale molecular 3D structure into a good candidate for host-guest chemistry. The interaction between this nanocage and different guest molecules has been studied by means of NMR, UV/Vis, ESI-MS, and DOSY experiments, from which highly selective molecular recognition has been found for anionic, planar-shaped π guests with association constants (K(a)) higher than 10(9) M(-1) , in front of non-interacting aromatic neutral or cationic substrates. DFT theoretical calculations provided insights to further understand this strong interaction. Nanocage 3·(CF(3)SO(3))(8) can not only strongly host one single molecule of M(dithiolene)(2) complexes (M=Au, Pt, Pd, and Ni), but also can finely tune their optical and redox properties. The very simple synthesis of both the supramolecular cage and the building blocks represents a step forward for the development of polyfunctional supramolecular nanovessels, which offer multiple applications as sensors or nanoreactors.