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)3·2H2O (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)3TEMPO-CN] n for Ln = GdIII and TbIII, whereas zero-dimensional complexes of the formula [Dy(hfac)3(TEMPO-CN)2][Dy(hfac)3(H2O)2]2 are obtained for Ln = DyIII. 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 JGd-rad/ kB = -21.18 K, 14.72 cm-1 ( H = - JSrad SGd spin Hamiltonian convention). The TbIII derivative, Tb-TEMPO-CN, also shows strong Tb-radical AF coupling, which has been rationalized using the ab initio CASSCF approach ( JTb-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 ( Ueff = 69.3 ± 1 K; τ0 = 1.3 × 10-7 s) and two different relaxation processes triggered by interchain magnetic coupling.