Magnetic Slow Relaxation in Cyclic Tb III ‐Nitronyl Nitroxide Radical Complexes

Two nitronyl nitroxide radical‐Tb III complexes, [Tb(hfac) 3 (NIT‐3Py)] 2 ( 1 ) and [Tb(hfac) 3 (NIT‐4Py)] 2 ( 2 ) {hfac = hexafluoroacetylacetonate; NIT‐3Py = 2‐(3′‐pyridyl)‐4,4,5,5‐tetramethylimidazoline‐1‐oxyl 3‐oxide; NIT‐4Py = 2‐(4′‐pyridyl)‐4,4,5,5‐tetramethylimidazoline‐1‐oxyl 3‐oxide} have been synthesized. Both complexes possess cyclic dimer structure in which each pyridyl‐substituted radical links two different metal ions through the oxygen of nitroxide group and the pyridine nitrogen. DC magnetic studies show the Tb III ion interacts ferromagnetically with the directly bonding nitronyl nitroxide. Complex 1 exhibits magnetic slow relaxation resembling SMM behavior, while there are no clearly the frequency‐dependent out‐of‐phase signals for complex 2 .(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)