GADOLINIUM(III) COMPLEXES WITH PYRIDINE-SUBSTITUTED NITRONYL NITROXIDE RADICALS

Two compounds of formula Gd(hfac)3(NIToPy).0.5C7H16 (I) and Gd(hfac)3(NITpPy) (II), respectively, where hfac = hexafluoroacetylacetonate, NIToPy = 2-(2-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl 3-oxide, and NITpPy = 2-(4-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl 3-oxide, have been synthesized. Compound I crystallizes in the monoclinic space group P2(1)/n with a = 1642.4 (4) pm, b = 1300.8 (8) pm, c = 2089.4 (4) pm, beta = 109.85 (2)-degrees, Z = 4, R = 0.0668, and R(w) = 0.0711. The structure consists of isolated molecules where the nitronyl nitroxide radical acts as a bidentate ligand toward gadolinium(III) through the nitrogen atom of the pyridine ring and the oxygen atom of the N-O group. Compound II crystallizes in the monoclinic space group P2(1)/n with a = 1709.9 (4) pm, b = 1222.2 (6) pm, c = 1850.2 (5) pm, beta = 93.01 (2)-degrees, Z = 4, R = 0.0432, and R(w) = 0.0464. In the solid state a NITpPy molecule is bound through the pyridine nitrogen to a Gd(hfac)3 molecule and through the oxygen of the N-O group to gadolinium(III) of another asymmetric unit. In this way molecules are formed where two gadolinium(III) and two nitronyl nitroxide radicals are present. The magnetic properties of both the complexes were studied by measuring their magnetic susceptibilities at various temperatures in the 1.6-300 K range. The analysis of these data showed that a ferromagnetic coupling between the lanthanide ion and the radical is always present. This result is discussed on the basis of magnetic exchange through a spin polarization mechanism.