Supramolecular self-assembly of a certain number of designer organic/inorganic building blocks by directional interactions such as metal coordination is the basis of elaborate molecular systems. Most molecular architectures are purpose-designed in light of the size, shape, and surface natures of building blocks as well as chemical environments. On the other hand, we have occasionally come across unexpected structures and functions as a result of more complicated self-assembly processes than expected, which have often opened a new frontier in chemistry. We have been focusing on coordination-driven self-assembly directed toward artificial metallo-DNAs,1,2 metallo-containers,3,4 molecular ball bearings,5 molecular gearing systems,6 and metal macrocycle frameworks (MMFs).7.8 This paper describes supraspace chemistry taking an example of a supramolecular porous crystal, MMFs, which provides a confined nano-space for molecular recognition and transformation.

Proton-coupled electron transfer (PCET), in which a proton and an electron are directed to respective accepting sites separately, is a fundamental process as observed in many kinds of redox reactions including biological and chemical processes. PCET oxidation of Ru(II)-aqua complexes has been applied for the formation of Ru(IV)-oxo, Ru(III)-hydroxo, and novel Ru(III)-oxyl complexes as reactive species in oxidation reactions of organic substrates and mechanistic insights into the reactions are gained on the basis of kinetic analysis. Ru(III)-pterin complexes without oxo ligands can accept hydrogen from O–H and C–H bonds of substrates and the reactivity and transition states of hydrogen-atom transfer reactions are revealed to be controlled by the proton acceptability and electron acceptability of the hydrogen acceptors; this is also valid for Ru(IV)-oxo complexes. Intramolecular PCET also enables to establish novel molecular bistability to regulate the direction of electron transfer and to create unprecedented electronic structures of metal complexes.

Coordination nanomaterials, which are made from a bottom-up assembly of metal ions and organic ligands, have been of particular interest to researchers because of their high degrees of structural designability and tunability based on substitutions of their structural components. In this review, successful fabrications and electronic and physical properties of mixed-valence multi-legged ladder complexes and crystalline oriented metal–organic framework (MOF) thin films, which straddle among one-, two-, and three-dimensional systems are described. Their unique electronic properties depending on the number of constituent legs and downsizing effects on physical properties have recently been overviewed.

In this article, recent developments regarding the organometallic chemistry of boron-containing pincer ligands, especially in which a boron coordinated to transition metal center as an anionic σ-donor ligand, are reviewed. Boron-based pincer ligands can be subdivided into three main classes; diazaborole-, carborane-, and diarylboryl-ligand. All the papers relevant to such boron-based pincer ligands that have been published since 2009 are included in this review, which also summarizes applications of transitionmetal complexes bearing such boron-containing pincer ligands in catalytic and/or bond-cleavage reactions.