A Diruthenium Complex of an N-Pyridyl-o-aminophenol Derivative: A Route to Mixed Valency

An N-pyridyl-o-aminophenol derivative that stabilises mixed-valence states of ruthenium ions is disclosed. A diruthenium complex, [(L-IQ(0))Ru2Cl5].MeOH (1.MeOH) is successfully isolated, in which L-IQ(0) is the o-iminobenzoquinone form of 2-[(3-nitropyridin-2-yl)amino]phenol (LAPH2). In 1, L-IQ(0) oriented towards one ruthenium centre is a non-innocent NO-donor redox ligand, whereas another oriented towards another ruthenium centre is an innocent pyridine-donor redox ligand. Complex 1 is a diruthenium(II,III) mixed-valence complex, [Ru-II(L-IQ(0))(mu-Cl)(2)Ru-III], with a minor contribution from the diruthenium(III,III) state. [Ru-III(L-ISQ(.-))(mu-Cl)(2)Ru-III] contains L-ISQ(.-), which is the o-iminobenzosemiquinonate anion radical form of the ligand. Complexes 1(-) and 1(+) are diruthenium(II,II), [Ru-II(L-IQ(0))(mu-Cl)(2)Ru-II], and diruthenium(III,III), [Ru-III(L-IQ(0))(mu-Cl)(2)Ru-III], complexes, respectively, of L-IQ(0). Complex 1(2-) is a diruthenium(II,II) complex of the o-iminobenzosemiquinonate anion radical (L-ISQ(.-)), [Ru-II(L-ISQ(.-))(mu-Cl)(2)Ru-II], with a minor contribution from the diruthenium(III,II) form, [Ru-III(L-AP(2-))(mu-Cl)(2)Ru-II]. Complex 1(2+) is a diruthenium(III,IV) mixed-valence complex of L-IQ(0), [Ru-III(L-IQ(0))(mu-Cl)(2)Ru-IV]. Complexes 1 and 1(2+) exhibit inter-valence charge-transfer transitions at lambda=1300 and 1370 nm, respectively.