Molecular approaches to photomagnetic materials. Metal-dependent regiospecificity in the exchange coupling of magnetic metal ions with the free radical substituents on pyridine base ligands

Coordinatively unsaturated Cr(III), Mn(II) and Cu(II) complexes form with N-tert-butyl-N-(3- and 4-pyridyl)aminoxyls discrete complexes in which the pyridyl nitrogen atoms are coordinated to the metal ions. Magnetic susceptibility measurements revealed that the intramolecular exchange coupling between the magnetic metal ions and the aminoxyl group in the complexes is governed not only by the orientation of the pi-spin-polarized pyridyl ring but also on the nature of the magnetic d-orbital of the metal ions. One-to-one chain polymer complexes were obtained from bis(hexafluoroacetylacetonato)manganese(II) and copper(II) with diazodi(4-pyridyl)methane. The weakly paramagnetic complexes were converted to ferri- and ferromagnetic chains, respectively, of considerable correlation length upon UV-irradiation.