Coordination compounds containing three different spin carriers (2p, 3d, and 4f), with the general formula [(MDyIII)-Dy-II(LH)-(hfac)(5)] (M = Co, Ni, Mn, Zn), have been obtained using Mannich ligands decorated with a nitronyl-nitroxide fragment. The synthetic approach is general and leads to binuclear 3d-4f complexes, the two metal ions being bridged by one aminoxyl group and by one oxygen atom arising from a hfac(-) ligand. Triangular spin topology affords significant 2p-3d, 3d-4f, and 2p-4f exchange interactions. For the [Co(II)Dy(III)Rad] derivative obtained using a nitronyl-nitroxide chiral ligand, a high energy barrier (similar to 200 cm(-1)) and a slow relaxation behavior below 30 K were found and rationalized by ab initio calculations. The improvement of magnetic properties comes from the synergy of optimal single ions properties and exchange couplings contributions where the Co-II-Rad interaction becomes the leading one. The role played by this interaction is clearly proved by the investigation of the magnetic properties of the [Zn(II)Dy(III)Rad] derivative, with a much lower energy barrier (12.7 cm(-1)) and by the lack of SMM behavior of the previously reported [Co(II)Dy(III)Rad] compound (Chem. Commun. 2017, 53, 6504), with a linear topology of spin carriers and a negligible Co-II-Rad interaction.