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

Abstract

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)₂1 complex while the reaction with the azido anion (N₃⁻) leads to the [Ru(salen)(PPh₃)(N₃)] 2 complex (where salen²⁻ = 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 salen²⁻ 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 π-stacking in pairs. While antiferromagnetic intermolecular interaction (J₂ = 5.0 cm⁻¹) dominates at low temperatures, ferromagnetic intramolecular interaction (J₁ = −9.0 cm⁻¹) have been found between the Ru(III) ion and the coordinated NITpPy.