Strong exchange couplings in lanthanide complexes with an aliphatic nitroxide radical 1,1,3,3-tetramethylisoindolin-2-oxyl

Abstract

We prepared crystalline [REIII(hfac)3(TMIO)2] (RE=Gd, Y; abbreviated as RE-TMIO2), where TMIO and hfac stand for 1,1,3,3-tetramethylisoindolin-2-oxyl and 1,1,1,5,5,5-hexafluoropentane-2,4-dionate, respectively. Two compounds are isomorphous in a C2/c space group. The paramagnetic TMIO ligand serves as an O-donor, and there are two TMIO moieties related with twofold symmetry in each molecule. The discrete molecular system guarantees the three- or two-centered exchange-coupling model. Magnetic study clarified that Gd-TMIO2 behaved as a ground Stotal=5/2 species with the intramolecular exchange couplings 2JGd-TMIO/kB=−12.5(4)K and 2JTMIO–TMIO/kB=−27(2)K from an isosceles triangle model. Superexchange interaction across the diamagnetic Y ion was characterized in Y-TMIO2 with 2JTMIO–TMIO/kB=−21.3(2)K from the singlet–triplet model. DFT calculation on Y-TMIO2 and a series of model compounds involving Rb+, Sr2+, Y3+, and Zr4+ suggests a possible mechanism involving ligand-to-metal charge transfer interaction for the relatively strong radical–radical couplings.