Two mononuclear complexes [(Et₃NH)[M(hfac)₂L] (M = Ni, 1; Zn, 2) have been synthesized using a nitronyl-nitroxide radical substituted nitrophenol, that is 2-(2-hydroxy-3-methoxy-5-nitrophenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-3-oxide-1-oxyl, HL, as a proligand. The crystal structures of 1 and 2 have been solved and indicate an octahedral coordination geometry of the metal ions. The magnetic behavior for 1 is characterized by a strong antiferromagnetic metal–radical interaction (J = −351 ± 1 cm⁻¹; H = −JS _Ni S _Rad). This exchange interaction was rationalized by DFT calculations. The EPR spectra recorded in both solution and solid state at 120 K confirm the S = ½ ground state for 1.