Pathway selection in the self-assembly of Rh4L4 coordination squares under kinetic control

Pathway selection principles in reversible reaction networks such as molecular self-assembly have not been established yet, because achieving kinetic control in reversible reaction networks is more complicated than in irreversible ones. In this study, we discovered that coordination squares consisting of cis-protected dinuclear rhodium(II) corner complexes and linear ditopic ligands are assembled under kinetic control, perfectly preventing the corresponding triangles, by modulating their energy landscapes with a weak monotopic carboxylate ligand (2,6-dichlorobenzoate: dcb-) as the leaving ligand. Experimental and numerical approaches revealed the self-assembly pathway where the cyclization step to form the triangular complex is blocked by dcb-. It was also found that one of the molecular squares assembled into a dimeric structure owing to the solvophobic effect, which was characterized by nuclear magnetic resonance spectroscopy and single-crystal X-ray analysis.

Efficient water-based purification of metal-organic polyhedra by centrifugal ultrafiltration

An efficient water-based purification strategy for metal-organic polyhedra (MOPs) using commercially available centrifugal ultrafiltration membranes was developed. Having a diameter above 3 nm, MOPs were almost fully retained by the filters, while free ligands and other impurities were washed away. MOP retention also enabled efficient counter-ion exchange. This method paves the way for the application of MOPs with biological systems.

Water-Soluble Ionic Metal-Organic Polyhedra as a Versatile Platform for Enzyme Bio-immobilization

Metal-organic polyhedra (MOPs) can act as elementary structural units for the design of modular porous materials; however, their association with biological systems remains greatly restricted by their typically low stabilities and solubilities in water. Herein, we describe the preparation of novel MOPs bearing either anionic or cationic groups and exhibiting a high affinity for proteins. Simple mixing of the protein bovine serum albumin (BSA) and ionic MOP aqueous solutions resulted in the spontaneous formation of MOP-protein assemblies, in a colloidal state or as solid precipitates depending on the initial mixing ratio. The versatility of the method was further illustrated using two enzymes, catalase and cytochrome c, with different sizes and isoelectric points (pI's) below and above 7. This mode of assembly led to the high retention of catalytic activity and enabled recyclability. Furthermore, the co-immobilization of cytochrome c with highly charged MOPs resulted in a substantial 44-fold increase of its catalytic activity.

Post-synthetic modifications of metal–organic cages

Metal-organic cages (MOCs) are discrete, supramolecular entities that consist of metal nodes and organic linkers, which can offer solution processability and high porosity. Thereby, their predesigned structures can undergo post-synthetic modifications (PSMs) to introduce new functional groups and properties by modifying the linker, metal node, pore or surface environment. This Review explores current PSM strategies used for MOCs, including covalent, coordination and noncovalent methods. The effects of newly introduced functional groups or generated complexes upon the PSMs of MOCs are also detailed, such as improving structural stability or endowing desired functionalities. The development of the aforementioned design principles has enabled systematic approaches for the development and characterization of families of MOCs and, thereby, provides insight into structure-function relationships that will guide future developments.

Novel Porous Rhodium Metal-Organic Aerogel for Efficient Removal of Organic Dyes and Catalysis of Si-H Insertion Reactions

Metal-organic gels (MOGs) are attracting increasing attention for removal of organic dyes from aqueous solution and for catalysis of Si-H insertion reactions. Herein, we report that a reaction of porphyrin derivative 1 with Rh₂(OAc)₄ generates stable metal-organic gels and subsequent subcritical carbon dioxide drying affords metal-organic aerogels. Owing to their micro- and mesoporosity, the aerogels adsorbed dyes. Moreover, aerogel I catalyzed Si-H insertion reactions to give organosilicon compounds in high yields.

Preparation of a magnetic metal-organic square and metal-organic cubes using 4,5-bis(2-imidazolinyl)imidazolate: slow magnetization relaxation behavior in mixed-valent octamanganese(ii/iii) clusters

Functional metal-organic squares (MOSs) and metal-organic cubes (MOCs) are important building units for zeolite-like metal-organic frameworks (ZMOFs), which are required to exhibit solid-state properties, such as dielectric, conductive, and magnetic properties. This work describes the preparation and magnetism of a tetracopper(ii) macrocyclic complex [Cu^II₄(im-H₂bizn)₄(DMSO)₃(THF)](ClO₄)₄·8DMSO (1) (Him-H₂bizn = 4,5-bis(4,5-dihydro-1H-imidazol-2-yl)imidazole) as a MOS and octametallic clusters [Ni^II₈(im-H₂bizn)₁₂](ClO₄)₄·10MeOH·3H₂O (2) and [Mn^II₄Mn^III₄(im-H₂bizn)₁₂](ClO₄)₈·14MeOH (3) as MOCs. The Cu^II ion in 1 possesses a five-coordinated square pyramidal geometry, resulting in the formation of an M₄L₄-type square, which gives an estimated intramolecular antiferromagnetic interaction with an exchange coupling constant of J_Cu-Cu = -95 K. Meanwhile, 2 and 3 present six-coordinated octahedral geometries, giving M₈L₁₂-type cubes, of which 2 is a normal paramagnetic compound with intramolecular antiferromagnetic interactions, and where J_Ni-Ni = -32 K. The most notable compound 3 is a Mn^II₄Mn^III₄ mixed valence state compound, which exhibits a slow magnetization relaxation behavior similar to that of single-molecule magnets. This is attributed to the contribution of magnetic anisotropy caused by the Jahn-Teller effect of the Mn^III ions. Utilizing a modified Arrhenius plot to extract the values of the thermal barrier for magnetization reversal (E_a/k_B) and the pre-exponential factor (τ₀), the parameters for the relaxation behavior were estimated to be E_a/k_B = 6.38 K and τ₀ = 3.87 × 10^-7 s. UV-vis spectroscopy and electrochemical measurements in solution were also carried out. Compound 3 will be expected to lead to a solid-state material in which the magnetic and dielectric properties of encapsulated small molecules cooperate with the slow magnetization relaxation properties of the MOC backbone.