Investigation of magnetic interaction pathways by experimental electron density measurements: application to an organic free radical, p-(methylthio)phenyl nitronyl nitroxide

The [X − (X + N)] electron density distribution in a 3D ferromagnetic purely organic free radical, p-(methylthio)phenyl nitronyl nitroxide, is reported and analysed in terms of magnetic interactions. From the atomic charges obtained by multipolar refinement against the X-ray data, a charge transfer by intermolecular hydrogen bonds between the O–N–C–N–O fragment of the nitronyl ring and the methylthio group is pointed out. Rotation of the oxygen lone pairs is also observed in the direction corresponding to short intermolecular N–O···O–N contacts. The topological analysis of the electron density allows us to characterise the bonding scheme in this radical and clearly demonstrates an electron delocalisation from the two oxygen to the sulfur atom through the phenyl ring. The atomic vibrations are investigated and their influence on the intermolecular interactions is discussed.