Ferromagnetic interactions in Ru(III)-nitronyl nitroxide radical complex: a potential 2p4d building block for molecular magnets

The reaction between [Ru(salen)(PPh3)Cl] and the 4-pyridyl-substituted nitronyl nitroxide radical (NITpPy) leads to the [Ru(salen)(PPh3)(NITpPy)](ClO4)(H2O)(2) 1 complex while the reaction with the azido anion (N-3(-)) leads to the [Ru(salen)(PPh3)(N-3)] 2 complex (where salen(2-) = N,N'-ethan-1, 2-diylbis(salicylidenamine) and PPh3 = triphenylphosphine). Both compounds have been characterized by single crystal X-ray diffraction. The two crystal structures are composed by a [Ru(III)(salen)(PPh3)](+) unit where the Ru(III) ion is coordinated to a salen(2-) ligand and one PPh3 ligand in axial position. In 1 the Ru(III) ion is coordinated to the 4-pyridyl-substituted nitronyl nitroxide radical whereas in 2 the second axial position is occupied by the azido ligand. In both complexes the Ru( III) ions are in the same environment RuO2N3P, in a tetragonally elongated octhaedral geometry. The crystal packing of 1 reveals p-stacking in pairs. While antiferromagnetic intermolecular interaction (J(2) = 5.0 cm(-1)) dominates at low temperatures, ferromagnetic intramolecular interaction (J(1) = -9.0 cm(-1)) have been found between the Ru(III) ion and the coordinated NITpPy.