Isolation of a Pentadentate Ligand and Stepwise Synthesis, Structures, and Magnetic Properties of a New Family of Homo- and Heterotrinuclear Complexes

A neutral pentadentate ligand, di(pyrazolecarbimido)amine (Hdcadpz), and its adduct with HClO4, [H2dcadpz]+[ClO4]-, were for the first time isolated from our previously reported [Cu3(dcadpz)2(Hpz)2(ClO4)2](ClO4)2·H2O by the use of (NH4)2S to remove the CuII ions and characterized by IR, EA, UV, NMR, MS, and X-ray crystallography. Reactions of copper(II) or nickel(II) nitrate with Hdcadpz in a 1:2 molar ratio generated two mononuclear precursors of [Cu(dcadpz)2] (1) and [Ni(dcadpz)2]·2/3DMF (2). Furthermore, three new linear homo- and heterotrinuclear complexes of the same motif [M{M‘(dcadpz)2}M] (M = CoII, NiII, M‘ = CuII, NiII), [{Co(pdm)}2{Cu(dcadpz)2}](NO3)4 (3), [{Ni(pdm)}2{Cu(dcadpz)2}](NO3)4 (4), and [{Ni(MeOH)(H2O)2}2{Ni(dcadpz)2}](NO3)4 (5), were synthesized from these two precursors (pdm = 2,6-pyridinedimethanol) and characterized by X-ray crystallography. Magnetic studies show that the central Cu(dcadpz)2 motif is antiferromagnetically coupled with both the terminal Co(II) atoms via the dcadpz- ligand in 3 with a J value of −5.27 cm-1 and ferromagnetically coupled with both the terminal Ni(II) atoms in 4 with a J value of 2.50 cm-1, while 5 behaves only as a Curie paramagnet between 2 and 300 K due to the diamagnetic character of the central square-planar Ni(II) atom.