Synthesis, crystal structure, electrochemical, EPR and magnetic properties of dinuclear complexes with an Okawa-style unsymmetrical diphenolato Schiff base macrocyclic ligand

Three dimetallic complexes of the unsymmetrical macrocycle (L)2−, [M1M2L]2+ (M1M2 = NiNi, CuZn, CuCd), have been synthesized by cyclocondensation between N,N′-bis(3-formyl-4-n  -butylsalicylidene)ethylenediimine and 1,3-diaminopropane in the presence of M12+ and M22+.The crystal structure of the complex [Ni2L4(H2O)2](ClO4)2 · 0.5CH3OH was determined by X-ray diffraction techniques.The asymmetric unit contains two complete macrocyclic complexes which are nevertheless quite similar to one another.The nickel–nickel separations, bridged by the two phenoxides, are 2.977 Å and 2.982 Å.In each molecule, the Ni(II) located in the ethylene chain linked site has a square planar geometry whereas the Ni(II) located in the propylene chain linked site has an octahedral environment.The results of ES-MS and cycle voltammograms confirm that Cu–Zn, Ni–Ni form stable complexes with the macrocyclic ligand L, however the complex composed of Cu–Cd was unstable, and easily lost Cd2+ from the complex in methanol solution.The cyclic voltammograms of the complexes show that each complex undergoes a stepwise reduction process, e.g.[Ni2L]2+ with E1/21=-0.862V and E1/22=-1.20V.Magnetic measurements in the 2–300 K range indicate weak antiferromagnetism for the dinuclear nickel(II) complex with the exchange constantJ = −0.90 cm−1.

Graphical abstractThree unsymmetrical dinuclear macrocyclic complexes have been synthesized.One structure was determined by X-ray diffraction.Each complex undergoes a stepwise reduction process, e.g.[Ni2L]2+ with E1/21=-0.862V and E1/22=-1.20V.Magnetic measurements in the 2–300 K range indicate weak antiferromagnetism for the dinuclear nickel(II) complex with the exchange constant J = −0.90 cm−1.Figure optionsDownload full-size imageDownload as PowerPoint slide