Magnetic study on radical-gadolinium(III) complexes. Relationship between the exchange coupling and coordination structure

Antiferro- and ferromagnetic couplings were observed in [Gd(hfac)(3)(2pyNO)(H2O)] and [Gd(hfac)(3)(-HNN)(2)], respectively, where 2pyNO stands for tert-butyl 2-pyridyl nitroxide and HNN for 4,4,5,5-tetramethylimidazolin-1-oxyl 3-oxide. The magnitude of the former is the largest in Gd-nitroxide complexes (2J/k(B) = -13.8(3) K). An empirical relation between the exchange coupling and torsion angle Gd-O-N-C is drawn, where large torsion (>36 degrees) favors ferromagnetic coupling. (C) 2013 Elsevier Ltd. All rights reserved.