From the viewpoint of molecular self-assembly, we have tackled unresolved issues in coordination chemistry. In this review, an overview of these studies will be presented. [1] Development of one-dimensional metal complexes whose electronic or spin structures are regulated based on self-assembly: By introducing synthetic lipids as counter anions of one-dimensional halogenbridged mixed-valence complexes, we have developed a methodology for dispersing one-dimensional complex chains as nanowires in organic solvents. Thermochromism was observed in organic solvents, indicating that one-dimensional electronic structures form in response to self-assembly. We also observed solvatochromism in the lipophilic metal complexes. In the linear Fe(II) triazole complexes, the low-spin state is specifically stabilized when dispersed in low-polarity solvents, and spin conversion was observed for the solution-dispersed nanowires. Furthermore, the first example of heat-set gel formation was found for Co(II) triazole complex in organic media. We found that the change in coordination structure leads to unique complex solution properties. [2] Discovery of dissipative nanostructures. [3] Adaptive self-assembly in aqueous coordination nanoparticles. [4] Development of photon upconversion molecular systems based on self-assembly. These studies have opened up a new research area between molecular organization chemistry and coordination chemistry, which would provide a basis for molecular systems chemistry.

Synthetic copper-dioxygen complex design, generation and characterization, play a crucial role in elucidating the structure/function of copper-based metalloenzymes, including dopamine β-monooxygenase, lytic polysaccharide monooxygenases, particulate methane monooxygenase, tyrosinase, hemocyanin, and catechol oxidase. Designing suitable ligands to closely mimic the variable active sites found in these enzymes poses a challenging task for synthetic bioinorganic chemists. In this review, we have highlighted a few representative ligand systems capable of stabilizing various copper-dioxygen species such as Cu^II-(O₂^•-)(superoxide), Cu₂^II-(μ-η¹:η¹-O₂^2-) (trans/cis-peroxide), Cu₂^II-(μ-η²:η²-O₂^2-) (side-on peroxide) and Cu_n^II-^–OOH (hydroperoxide)species. Here, we discuss the ligand type utilized, syntheses, and spectroscopic characterization of these species. We also delineate reactivity patterns, particularly electrophilic arene hydroxylation by a side-on peroxo species which occurs via a “NIH shift” mechanism and thermodynamic-kinetic relationships among Cu₂-(O₂^•-)/O₂^2-/ ^-OOH moieties.

Metal-organic frameworks (MOFs) have garnered significant interest in membrane-based separations due to their tunable porosity and customizable chemistry. To achieve optimal transport efficiency, researchers are striving to minimize membrane thickness to the greatest extent possible. This mini-review focuses on the development of ultrathin MOF membranes, emphasizing their enhanced separation performance. We discuss the advanced synthesis methods that allow for the precise control of MOF intergrowth, orientation, and flexibility, which are crucial for the fabrication of ultrathin and defect-free membranes. The review

highlights innovative approaches to stabilize ultrathin MOF layers, overcoming challenges related to their mechanical strength and scalability. We also explore the integration of MOF membranes into existing industrial processes, showcasing their efficiency in energy-intensive separations. The review concludes with a perspective on the future directions of MOF membrane research, including the need for large-scale production techniques and the exploration of new fabrication methods for targeted separation tasks. This mini-review serves as a guide for researchers in the field of membrane technology, offering insights into the current state and future possibilities of ultrathin MOF membranes in separation applications.

In this study, we focused on analyzing metal clusters at the atomic level using electron microscopy. Through advanced structural analysis techniques, we discovered various properties and phenomena in sub-nanometer clusters that were previously unknown in larger nanoparticles. Our findings revealed the concept of “sub-nanoalloying,” where different elements mix at the atomic level, resulting in enhanced catalytic performance. We also investigated the behavior and movements of these clusters to understand their stability and reactivity. Our findings have implications for designing advanced materials with tailored properties and improved catalytic applications.

Porous coordination polymers (PCPs), also known as metal-organic frameworks (MOFs), constitute a class of crystalline framework materials formed through the coordination of metal clusters and organic ligands. Within this category, there exist structurally responsive PCPs, commonly referred to as flexible PCPs, which can manifest intriguing structural properties. This ability stems from their capacity to adopt multiple interchangeable structures contingent upon external factors such as temperature, pressure, and the presence of guest molecules. We have successfully synthesized and characterized various flexible PCPs demonstrating distinctive sorption/separation, catalysis, and sensing properties, all attributable to their flexible nature. We extensively employ in-situ and operando measurements to elucidate their structural and functional properties. In this account, we outline our recent advancements in functional flexible PCPs based on an innovative design approach. These advancements encompass the creation of multistable activation structural phases, water isotopologue separation, exclusive CO₂ separation, control of catalysis, and modulation of chemiresistivity through orientation control of PCP films.

Molecular self-assembly has recently developed to create a variety of three-dimensional giant architectures, being reminiscent of large biomolecules. Coordination-driven self-assembly, particularly, is one of the sophisticated approaches to build up brilliant structures with remarkable chemical and physical properties, owing to the moderate reversibility and high directionality of the coordination bonds toward a formation of a defined structure. In contrast to the rich examples of the metal–ligand assemblies, supramolecular complexes based on noncovalent interactions have been less explored. In this paper, our recent results on molecular assemblies using a hydrogen-bonding organic host and coordination complexes are summarized. The components were strongly bound each other by concerted effects of noncovalent interactions, forming unique host–guest complexes. Thanks to the high flexibility and adaptivity of the driving forces, the self-assembled product gained remarkable complexity and functionality. The molecular assembly of the organic hosts and coordination complexes via heterogeneous conditions also afforded supramolecular structures in “out-of-equilibrium” state. These findings based on this molecular system will endow us with a chance to encounter many serendipities and provide useful materials originating from the unique structures.

Photovoltaic cells using metal halide perovskite crystals as semiconductors have achieved sunlight power conversion efficiency exceeding 26% comparable to the top efficiency of crystalline silicon solar cells. A key process of the device fabrication that affects device performance is the coating of source materials organic solution and subsequent crystallization of perovskite that forms a thin polycrystalline film (<1 mm). Therefore chemical processes that control the intermediate complexes are important for high-quality film capable of high efficiency. In this review, mechanism of crystallization and the method to enhance the photovoltaic performance of the perovskite solar cell by chemical passivation of crystal interfaces are discussed, focusing on improvement of photovoltage output by way of minimizing defect-assisted charge recombination at the interfaces.

This review article reports several theoretical/computational approaches to coordination chemistry. First, spin state and M-M multiple bonding of dinuclear and trinuclear transition metal complexes are discussed on the basis of electronic structures obtained by multi-reference wave-function theory. In a cuboctahedral Pd13 cluster complex, theoretical knowledge obtained by DFT calculations is presented on determining factor(s) of its highly symmetrical structure. In theoretical studies of catalysis which is one of important functions of transition metal complexes, discussion is presented on how to understand key intermediates, transition states, and reaction mechanisms from the viewpoint of ligand field theory. Transition metal complexes in crystal exhibit interesting properties different from those in solution. Isomerization reaction and emission spectrum of transition metal complexes in crystal are discussed using theoretical calculations incorporating crystal effects. Gas adsorption to flexible porous-coordinationpolymers (PCPs) is investigated using a computational method consisting of DFT calculations of infinite system and post Hartree-Fock ones of cluster model. This computational approach succeeded in elucidating the origin of gate-opening gas adsorption mechanism and unusual sigmoidal adsorption isotherm.