Three novel gadolinium(III) radical complexes [Gd-III(hfac)(3)(H2O)(L)] [Gd-L; L = tert-butyl phenyl nitroxide (phNO) and its derivatives (tert-butyl 3-tolyl nitroxide and tert-butyl 4-tert-butylphenyl nitroxide)] were synthesized, and all compounds showed ferromagnetic coupling, obeying the empirical relation: out-of-plane coordination of the Gd ion from the radical pi system favors ferromagnetic coupling. In particular, Gd-phNO has a considerably large torsion angle around Gd-O-N-C-sp(2) (69.8(9)degrees on average) and the largest ferromagnetic coupling parameter (2J/k(B) = +18.0(4) K) in Gd nitroxide compounds ever known. The validity of our molecular design was assessed on the basis of the magneto-structure relation analysis with many literature data including various paramagnetic ligating groups.