RuII

RuII, written as Ru(II), designates ruthenium in the +2 oxidation state. In coordination chemistry, Ru(II) centers are common and typically adopt octahedral geometries with a low-spin d6 electronic configuration. They form stable complexes with a range of ligands, especially polydentate nitrogen donors such as 2,2'-bipyridine (bpy), 1,10-phenanthroline (phen), and terpyridine (tpy). The Ru(II) center is relatively inert to ligand substitution when bound to strong-field chelating ligands, though substitutions can occur under forcing conditions or with labile sites.

A widely studied class is the trisbipyridyl complex [Ru(bpy)3]2+, which serves as a benchmark in photochemistry and photophysics. Ru(II) polypyridyl complexes exhibit strong absorption in the visible region and can emit light from metal-to-ligand charge transfer (MLCT) excited states. Their excited-state lifetimes range from nanoseconds to microseconds and can be tuned by modifying ligands, affecting both emission color and redox properties.

Applications and research areas include photocatalysis, solar energy conversion, and dye-sensitized solar cells, where Ru(II) complexes can act as photosensitizers or mediators of electron transfer. They are also explored as luminescent probes for bioimaging and as components in light-activated catalysts. Ongoing work investigates broader catalytic applications, energy storage concepts, and sustainable synthesis leveraging the tunable photophysical and electrochemical properties of Ru(II) systems.