Rational enhancement of the coordination capability of Ru(III)(salen)-nitronyl nitroxide building block: A step towards 2p-3d-4d magnetic edifices

The reaction of [Ru(salen)(PPh3)Cl] and the 5-imidazol-substituted nitronyl nitroxide radical (NIT(5)ImH) yields the [Ru(salen)(PPh3)(NIT-(5)ImH)](ClO4) (1) complex which has been characterized by single crystal X-ray diffraction. This analysis reveals that the Ru(III) ion is coordinated to a tetradentate salen(2) ligand in equatorial positions while one PPh3 ligand and one NIT-(5) ImH radical are coordinated in axial positions. This led to Ru-III ions in tetragonally elongated octahedral geometry. From the magnetic point of view ferromagnetic intramolecular interaction (J(1) = + 2.47 cm (1)) have been found between the Ru(III) ion and the coordinated NIT-(5)ImH while no significant intermolecular antiferromagnetic interactions are observed at low temperature leading to a ground spin state S = 1. The absence of intermolecular magnetic interaction is explained by considering the crystal packing of (1) where the [Ru(salen)(PPh3)(NIT-(5)ImH)](+) moieties are relatively well isolated. This has to be compared with the situation observed in the previously reported [Ru(salen)(PPh3)-(NIT)](+) compound (2) where ferromagnetic Ru-III-NIT interaction were identified and the crystal packing generate intermolecular antiferromagnetic interactions that complicated the study. The analysis of this compound confirms the rather isotropic g values that were found of (2) and of [Ru(salen)(PPh3)(N-3)], (3) a radical-free analogue. Moreover it is also a step towards extended structures based on Ru-III-NIT moieties since this compound possesses a free bischelating site likely to coordinate additional metallic ions.