Proton dissociation of an aqua-Ru-quinone complex, [Ru(trpy)(3,5-t-Bu₂q)(OH₂)]²⁺ (trpy = 2,2’:6’,2”-terpyridine, 3,5-t-Bu₂q = 3,5-di-tert-butyl-1,2-banzoquinone) proceeded in two steps (pK_a = 5.5 and ca. 10.5). The first step simply produced [Ru(trpy)(3,5-t-Bu₂q)(OH)]⁺, while the second one gave an unusual oxyl radical complex, [Ru(trpy)(3,5-t-Bu₂sq)(O^-.)]⁰ (3,5-t-Bu₂sq = 3,5-di-tert-butyl-1,2-banzosemiquinone), due to an intramolecular electron transfer from the resultant O^2- to q. A dinuclear Ru complex bridged by an anthracene framework, [Ru₂(btpyan)(3,6-t-Bu₂q)₂(OH)₂]²⁺ (btpyan = 1,8-bis(2,2’:6’,2”-terpyrid-4'-yl)anthracene, 3,6-t-Bu₂q = 3,6-di-tert-butyl-1,2-banzoquinone), was prepared to place two Ru(trpy)(q)(OH) groups in a close distance. The [Ru₂(btpyan)(3,6-t-Bu₂q)₂(OH)₂](SbF₆)₂ modified ITO electrode effectively catalyzed four-electron oxidation of water to evolve O₂ (TON = 33,500) under the electrolysis at +1.70 V in H₂O (pH 4.0). Various physical measurements and DFT calculations indicated that a radical coupling between two Ru(sq)(O^-.) groups forms a (cat)Ru-O-O-Ru(sq) (cat = cathecholato) framework with a μ-superoxo bond. Deprotonation of an Ru-quinone-ammonia complex also gave the corresponding an Ru-semiquinone-aminyl radical. The oxidized form of the latter showed a high catalytic activity towards the oxidation of methanol in the presence of base.

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This review article gives an overview of our recent discovery that a Gemini-shaped hexa-peri-hexabenzocoronene (HBC) amphiphile (1) and its derivatives undergo highly controlled self-assembly to form a new family of nanotubes that may be called ‘graphite’ nanotubes. Compound 1 possesses hydrophilic triethylene glycol (TEG) chains on one side of the HBC core and hydrophobic dodecyl side chains on the other. The nanotubes are characterized by uniform diameter and wall thickness, a large aspect ratio, and designable inner and outer surfaces. Furthermore, they possess a helical chirality. In fact, under certain conditions, a coiled assembly, which is a kinetically preferred product, is formed temporarily and then transforms, on annealing, into a tubular assembly. Furthermore, HBC derivatives bearing a stereogenic center can form coiled and tubular assemblies with a one-handed helical chirality. Analogous to compound 1, HBC amphiphiles carrying functional groups at the TEG termini self-assemble in a highly controlled manner, affording surface-functional nanotubes. As one of the ideal designs for photovoltaic materials with a nanometric size regime, photoconductive nanotubes with a coaxial configuration of the donor/acceptor heterojunction is highlighted.

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The present contribution reviews the synthesis and properties of complexes including redox-active dioxolene ligands as well as its analogues, diiminosemiquinonato, and dithiolene ligands. This review first summarizes the structural and electronic features of new molecular complexes as a building block for constructing electronically labile molecular assemblies. Ligand-based mixed valence (LBMV) state has been realized both in mononuclear chromium and pentanuclear cobalt complexes. Second topic will be on the construction of molecular assemblies integrated by intermolecular stacking or charge-transfer interactions, clusterization, and ligand-unsupported M-M bonds. The formation of a thin film which acts as an active layer of a field-effect transistor will also be described. Final attention is drawn to the use of the redox-active complexes for the construction of stimuli-responsive molecular assemblies. The review will demonstrate recent developments of molecular assemblies that show macroscopic phase transition or phase transformation triggered by intramolecular electron transfer or redox reaction in solid, liquid, and liquid crystals.

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In this article, gas inclusion phenomena for a flexible single-crystal host have been described. The synthesized single crystal hosts exhibit high flexibility and adjustability for the properties of adsorbed guests to realize the highly ordered gas inclusion state. Because the crystal remains intact under gas adsorption state, it is possible to analyze the resulting host-guest aggregate in great and accurate details by conventional single-crystal X-ray diffraction. Here, the relationship between incorporated gaseous guest and walls of pores cannot be compared to the contact between a ball and a flat surface, but to the atomic contact of a point (atom) to a point (atom), raising the necessity of regarding a gas adsorption state as a co-crystal state. The study of flexible single-crystal host system will contribute to clarify the mechanism of dynamic adsorption to develop the new functions from the view point of the host-guest chemistry. Furthermore, the homogeneity, anisotropy, integrity, transparency, etc. of crystal hosts would contribute to the advancing of new techniques for future society.

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This review describes a series of five-membered metallacyclic compounds of unsaturated carbon-carbon bonds, especially, 1-metallacyclopenta-2,3,4-trienes, 1-metallacyclopent-3-ynes and 1-metallacyclopenta-2,3-dienes on their syntheses, structures and reactivity. Five-membered cyclotrienes andcycloalkynes are prepared from group 4 metal and 1,3-diyne, 1,2,3-butatriene, although cycloallenes have not been synthesized from 1,3-enynes. 1-metallacyclopenta-2,3-dienes are prepared by a few unique methods. These compounds are remarkably stable in spite of their highly strained ring-structure.Some of their molecular structures were even determined by X-ray diffraction study. The 1-metallacyclopenta-2,3,4-trienes and 1-metallacyclopent-3-yneshave a planar metallacycle. The 1-metallacyclpenta-2,3-dienes, on the other hand, have a folded metallacycle and a chiral structure. Some reaction ofthese complexes with borane, aluminum hydride, transition metals and carbonyl compounds are described. Seven membered metallacyclic triene and alkyne areformed when 1,3-diyne or 1,2,3-butatriene coupled with other unsaturated hydrocarbons on the metal. Extended polyynes and cumulenes also form five-membered metallacyclotrienes and alkynes that show “haptotropic” shift.

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Real-time observations of ultrafast relaxation dynamics of metal complexes are very important for fundamental understanding of photo-excited states of this class of molecules. In these topics, some of the recent advances in the ultrafast time-resolved studies on metal complexes are introduced to treat with the behaviors in the time region of 10^-14 - 10^-12 s. Studies on fast relaxation dynamics of [Ru(bpy)₃]²⁺ (bpy = 2,2’-bipyridine), i.e., the intersystem crossing and electron localization dynamics in the MLCT exited state of the complex are discussed.

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