Synthesis and Electrochemistry of Organometallic Cobaltadithiaazulenes

Tris(tropolonato) ruthenium as a hub for connecting π-conjugated systems

In this study, the intramolecular electronic communication between π-conjugated moieties bridged by the tris-chelate [Ru(trop)₃] (trop = tropolonate) framework has been investigated and compared with [Ru(acac)₃] (acac = acetylacetonate) derivatives. Two types of π-conjugated groups, -C₂SiMe₃ and -C₂Ph, which were each introduced at the 5-position of tropolonate, were found to behave almost independently in the resultant ruthenium complexes. In contrast, the cyclic voltammetry study of [Ru(trop)₃] derivatives showed a clear decrease in ΔE, the difference in the potentials of the two redox couples, with an increase in the number of π-conjugated groups introduced into the [Ru(trop)₃] framework. The lower ΔE values observed in [Ru(trop)₃] derivatives compared to those in [Ru(acac)₃] derivatives illustrated the non-innocent behavior of the tropolonate ligand, i.e., the mixing between the metal- and ligand-based frontier orbitals. This orbital mixing was exemplified in the oxidized [Ru(trop)₃] derivatives, which showed a broad near-infrared (NIR) absorption. The increase in the red shift of the NIR absorption with the increasing number of terminal groups indicated intramolecular electronic communication between the terminal π-conjugated moieties. In contrast, no NIR absorption was observed upon oxidation of [Ru(acac)₃] derivatives with -C₂Ph groups. The lifetimes of the in situ formed [Ru(trop)₃]⁺ and [Ru(acac)₃]⁺ in acetonitrile solution were found to be several hours and minutes, respectively. Density functional theory calculations for [Ru(trop)₃] and [Ru(acac)₃] with terminal -C₂Ph groups demonstrated that the spin densities in their mono-oxidized states were evenly distributed over the entire molecular framework and localized mainly on one ligand, respectively. These results confirmed that the mono-oxidized [Ru(trop)₃]⁺ framework can behave as a hub and induce moderate intramolecular electronic communication between terminal π-conjugated groups.

Coordination Programming of Two-Dimensional Metal Complex Frameworks

Since the discovery of graphene, two-dimensional materials with atomic thickness have attracted much attention because of their characteristic physical and chemical properties. Recently, coordination nanosheets (CONASHs) came into the world as new series of two-dimensional frameworks, which can show various functions based on metal complexes formed by numerous combinations of metal ions and ligands. This Feature Article provides an overview of recent progress in synthesizing CONASHs and in elucidating their intriguing electrical, sensing, and catalytic properties. We also review recent theoretical studies on the prediction of the unique electronic structures, magnetism, and catalytic ability of materials based on CONASHs. Future prospects for applying CONASHs to novel applications are also discussed.