Coordination compounds containing three different spin carriers (2p, 3d, and 4f), with the general formula [M^IIDy^III(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^IIDy^IIIRad] derivative obtained using a nitronyl-nitroxide chiral ligand, a high energy barrier (∼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^IIDy^IIIRad] derivative, with a much lower energy barrier (12.7 cm^-1) and by the lack of SMM behavior of the previously reported [Co^IIDy^IIIRad] compound (Chem. Commun. 2017, 53, 6504), with a linear topology of spin carriers and a negligible Co^II-Rad interaction. Copyright