rutheniumII

Ruthenium(II) refers to the oxidation state of ruthenium in which the metal carries a +2 charge, commonly written as Ru(II). In this state, ruthenium typically has a d6 electronic configuration. In coordination chemistry, Ru(II) centers most often adopt octahedral or pseudo-octahedral geometries and form a wide range of complexes with nitrogen- and phosphorus-donor ligands, as well as carbonyls and halides.

Ru(II) complexes are frequently low-spin when ligands provide a strong crystal field, though some ligand environments can support higher spin. They are notable for their photophysical properties, especially when coordinated to polypyridine ligands, which generate metal-to-ligand charge transfer (MLCT) excited states that can be long-lived and highly radiative.

One of the best-known Ru(II) complexes is tris(bipyridine)ruthenium(II), [Ru(bpy)3]2+. This and related polypyridyl ruthenium(II) species are extensively studied as photoredox catalysts, luminescent probes, and sensitizers for dye-sensitized solar cells due to their visible-light absorption and accessible excited states.

In practical use, Ru(II) complexes contribute to catalysis, including hydrogen transfer reactions and various small-molecule activations, and serve a pivotal role in electrochemistry through Ru(II)/Ru(I) redox couples. They are typically prepared by coordinating ruthenium precursors to carefully chosen ligands under conditions that yield stable, often highly inert, octahedral coordination complexes.