Strong Magnetic Coupling and Single-Molecule-Magnet Behavior in Lanthanide-TEMPO Radical Chains

The rational design of molecular chains made of 4f ions and substituted 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical is presented. The reaction of Ln(hfac) 3 ·2H 2 O (hfac - = hexafluoroacetylacetonate) and the 4-cyano-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO-CN) radical affords air- and moisture-stable isostructural molecular chains of the formula [Ln(hfac) 3 TEMPO-CN] n for Ln = Gd III and Tb III , whereas zero-dimensional complexes of the formula [Dy(hfac) 3 (TEMPO-CN) 2 ][Dy(hfac) 3 (H 2 O) 2 ] 2 are obtained for Ln = Dy III . To the best of our knowledge, the Gd derivative, Gd-TEMPO-CN, shows one of the strongest antiferromagnetic (AF) couplings for Gd-radical pairs ever reported with J Gd-rad / k B = -21.18 K, 14.72 cm -1 ( H = - JS rad S Gd spin Hamiltonian convention). The Tb III derivative, Tb-TEMPO-CN, also shows strong Tb-radical AF coupling, which has been rationalized using the ab initio CASSCF approach ( J Tb-rad = -23.02 K, -16.7 cm -1 ) and confirmed by luminescence measurements. Tb-TEMPO-CN shows remarkable properties for a Tb-radical-based single-molecule magnet ( U eff = 69.3 ± 1 K; τ 0 = 1.3 × 10 -7 s) and two different relaxation processes triggered by interchain magnetic coupling.