Exchange-coupled terbium-radical complex Tb-phNO showing slow reversal of magnetization

Abstract

A novel terbium(III)-nitroxide complex [TbIII(hfac)3(phNO)(H2O)] (phNO=tert-butyl phenyl nitroxide, hfac=1,1,1,5,5,5-hexafluoropentane-2,4-dionate) was synthesized towards development of 4f-2p compounds with strong ferromagnetic exchange coupling. There are two crystallographically independent molecules in a unit cell. The ac magnetic susceptibility at Hdc=2000Oe showed double χm″ peaks accompanied by frequency dependence and afforded Ueff(1)/kB=46.3(7)K with τ0(1)=1.9(3)×10−9s for the high-temperature peak series and Ueff(2)/kB=21(2)K with τ0(2)=1.3(9)×10−8s for the low-temperature peak series. Every molecule is proven to behave as a potential single-molecule magnet (SMM). In contrast, the corresponding dysprosium(III) analogue did not exhibit meaningful out-of-phase ac magnetic susceptibility. In the strongly exchange-coupled regime owing to the direct radical coordination bond, the whole molecular electron counting may provide a useful criterion to predict Kramers molecules as potential SMM candidates.