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)center dot 2H(2)O (hfac(-) = hexafluoroacetylacetonate) and the 4-cyano-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO-CN) radical af-fords 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)(H2O)(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; tau(0) = 1.3 X 10(-7)s) and two different relaxation processes triggered by interchain magnetic coupling.