Magnetic bistability spanning over a temperature domain of 40 K can result from a small structural deformation of the gadolinium aminoxyl coordination. This is illustrated for a nitronyl nitroxide 3d-4f chain, [Ln(hfac)(3)Cu(hfac)(2)(NIT-Pyrim)(2)] (Ln(II) = Gd, Dy), which is the first example of a bistable lanthanide-based complex.