A metal complex may have flexible structure and electronic state which can be artificially modified and easily controlled. Such flexibilities can be useful tools for constructing functional moleclues. Since the discovery of metal-metal bonds in dinuclear metal complexes, multinuclear metal complexes have attracted intense research interests not only from syntheses but also chemical and physical properties. Such a complex shows more functions expected from just sum of components, one plus one can be more than 2. Our research has concerned with molecular magnetism of multinuclear complexes. In this article, chemistry of high spin molecules, quantum magnets, and switchable molecules is discussed.

Transition metal complexes have attracted considerable attentions because they show a variety of structures, reactivities, and properties. We have focused on the reactivity, especially the catalytic activity of iron complexes. An iron is an attractive precious metal surrogate because of its high natural abundance, low cost, and environmental compatibility. In this account, three topics concerning iron catalyst were selected from our results obtained. (i) An iron silyl complex can cleave a strong bond selectively. C-CN bonds in organonitriles, N-CN bonds in cyanamides, O-CN bonds in cyanates, Si-CN bonds in silylnitriles, C=O double bonds in formamides, and C=S double bonds in thioformamides were selectively cleaved with remaining weaker bonds intact. Silyl migration from iron serves as a trigger of the selective strong bond cleavage. (ii) Olefin hydrosilylation took place effectively in the presence of iron complex catalyst. Our system showed the highest catalytic activity among iron complex catalysts. In addition, an unprecedented hydrosilylation reaction was achieved by an iron complex catalyst. (iii) Catalytic double hydrophosphination promoted by an iron complex was developed. In this reaction, the starting phosphine and the diphosphine product did not serve as catalyst poison in the iron catalytic system.

Platinum(II) complexes have been extensively explored in previous years due to their intriguing chromphoric and aggregation properties. The introduction of supramolecular assembly components involving non-covalent interactions could lead to other dimensions of unlimited possibilities and opportunities. In this review, the utilization of this class of complexes in supramolecular assembly and various functions will be discussed. Examples include applications in ion-binding, solvent-induced aggregation, nucleic acid-induced aggregation responsive materials and light harvesting molecular devices. The unique features for this class of complexes could also be attributed to their versatile emissive excited states that are strongly affected by subtle changes in the local environment.

This article describes the recent research on molecular cages achieved in Nitschkeʼs group. Subcomponent self-assembly allows the construction of molecular cages from simple building blocks via the formation of coordination bonds and dynamic covalent bonds around metal templates. By utilizing this method, a variety of functional molecular cages have been constructed. In this article, we focused on two topics. In the first topic, molecular cages were utilized for the molecular recognition and the catalytic reaction. In the second topic, we describe the interesting nature of molecular cages that originates from reversible substitution of subcomponents of molecular cages.

Design of single-site photocatalysts (tetrahedral-coordinated metal oxide moiety, metal complexes) in nanoporous materials (zeolites, mesoporous silica, metal-organic frameworks) not only can promote unique photocatalytic reactions but also can be utilized to synthesize functional materials: visible-light sensitive single-site photocatalysts, nano-sized metal catalysts, superhydrophilic and superhydrophobic porous thin films. The unique and fascinating properties of silica-based zeolites, mesoporous silicas and metal-organic frameworks have opened up new possibilities for many chemical and physical processes. Because most of them are transparent to UV-visible light, these porous materials have often been functionalized with elements such as Ti, Cr, V, Mo, and W whose corresponding bulk oxides are known to be suitable photocatalysts. These well-defined active centers have shown to be highly dispersed at the atomic level in a tetrahedral-coordination geometry and have been named as “single-site photocatalysts”. These single-site photocatalysts not only can promote photocatalytic reactions but also can be utilized to synthesize functional materials. The plasmonic nano-metal particles and visible-light sensitive binary oxide photocatalyst can be synthesized on the excited single-site photocatalyst under light irradiation. The transparent mesoporous silica thin film with a single-site photocatalyst generates the super-hydrophilic surface. In this account, our applications of single-site photocatalysts to synthesis of the surface functional materials have been introduced.

Battery technology is a key to realize a sustainable society. The currently-used lithium-ion batteries, which were commercialized in 1991 by SONY, have high gravimetric/volumetric energy densities to power almost all the portable electronics. However, largescale applications such as electric vehicles or a power grid require development of better batteries, especially in terms of energy densities, power densities, cycle life, cost, and elemental strategy. Because the poor performance of the electrode materials is one of the main obstacles to the high-performance batteries, it is essential to discover novel electrode materials for advanced batteries. Herein, recent efforts devoted to application of coordination compounds to the battery electrodes are briefly summarized. In particular, the solid-state electrochemistry of cyano-bridged coordination compounds including Prussian blue analogs are focused.

In this review, dihydrogen and dioxygen activation by an oxygen-tolerant hydrogenase and its models is described. While a standard hydrogenase can only oxidize dihydrogen, the oxygen-tolerant hydrogenase can not only oxidize dihydrogen but also reduce dioxygen to water. The oxygen-tolerant hydrogenase is able to act as hydrogenase and oxidase, just like anode and cathode catalysts of fuel cell. We have completely reproduced the active-center structure and function of the oxygen-tolerant hydrogenase by using organometallic complexes for the first time and applied the organometallic complexes for fuel cell electrodes to construct "molecular fuel cell". The molecular fuel cell, which is fabricated by molecular catalysts as a model for the oxygentolerant hydrogenase, is capable of working to generate electricity from dihydrogen and dioxygen. The molecular catalysis gives a new strategy to construct the fuel cell system because it is flexible to design the structure and easy to understand the reaction mechanism by monitoring with various spectroscopies and mass spectrometries. The molecular approach is believed to open the door of new fuel cell in future.