ROLE OF HYDROGEN-BONDS IN THE PROPAGATION OF FERROMAGNETIC INTERACTIONS IN ORGANIC MOLECULAR-SOLIDS .1. THE P-HYDROXYPHENYL ALPHA-NITRONYL AMINOXYL RADICAL CASE

The role of hydrogen bonds in the obtention of magnetic molecular materials is investigated in a purely organic open-shell molecular solid. The structural and magnetic properties of the 2-(4-hydroxyphenyl)-4,4,5,5-tetramethyl-4,5-dihyro-1H-imidazol-yloxyl 3-oxide radical (1) are studied in detail. The intermolecular hydrogen bonds in 1 are found to be able to control the crystal packing (i.e. the relative disposition of the radical molecules within the crystal lattice) and, at the same time, to propagate ferromagnetic intermolecular interactions along certain directions of the solid. Molecular orbital (MO) calculations, structural studies about the crystal packing, static magnetic susceptibility measurements, electron paramagnetic resonance (EPR) solution spectra and a detailed EPR study of an oriented single crystal of the title compound are presented and discussed. All these studies point strongly towards the fact that this material behaves as a quasi-two-dimensional ferromagnet, in which hydrogen bonds of O-H...O-N and C-H...O-N types are found to be responsible for the transmission of the ferromagnetic interactions within the (a,b) crystallographic plane.