A novel trinuclear nickel(II) complex with N,N,N′,N″,N″‐pentamethyldiethylenetriamine (pmdien) and a trithiocyanurate(3–) (ttc3–) bridge of composition [Ni3(pmdien)3(μ‐ttc)](ClO4)3 (1) was prepared. The X‐ray crystal structure of 1 was determined, revealing the tris‐N,S chelating mode of the trithiocyanurate bridge, forming a regular triangular NiII3 core. A deformed trigonal bipyramidal arrangement of the central atoms was further achieved by coordination of three pmdien N atoms. The complex shows a ferromagnetic exchange interaction among the NiII magnetic centers that is tuned by single‐ion anisotropy and/or antisymmetric exchange. The complex orders ferromagnetically at Tc = 10 K and exhibits spin‐glass properties.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)