HexaaquarutheniumIII

Hexaaquaruthenium(III) is the hexaaqua cation [Ru(H2O)6]3+, a coordination complex of ruthenium in the +3 oxidation state. In this species, six water molecules surround the ruthenium center in an octahedral arrangement. The complex is typically formed and studied in aqueous, acidic solutions, where the hydration sphere remains intact. With increasing pH, it undergoes hydrolysis to form hydroxo-containing species, such as [Ru(H2O)5(OH)]2+, and further hydrolysis can lead to additional hydroxo or oxide species.

Spectroscopic and magnetic properties reflect its Ru(III) center, which is paramagnetic due to unpaired electrons in the d orbitals. The visible absorption of the aqua complex gives it characteristic coloration that depends on concentration, ligand field, and the presence of counterions. The chemistry of [Ru(H2O)6]3+ is influenced by pH, ionic strength, and the overall ligand environment, which can shift equilibria among aquated and hydroxo forms.

Reactivity and applications: the hexaaquaruthenium(III) ion functions as a Lewis acid and serves as a one-electron oxidant in redox chemistry (Ru(III)/Ru(II) couple). It is a common precursor to many ruthenium(III) coordination and organometallic complexes and is frequently encountered in studies of catalytic and electrochemical processes involving ruthenium. Although often examined in solution rather than isolated as a solid, [Ru(H2O)6]3+ provides a foundational example of Ruthenium(III) aqua chemistry and its pH-dependent speciation.