Polynuclear Ni(II)/Co(II)/Mn(II) Complexes Based on Terphenyl–Tetracarboxylic Acid Ligand: Crystal Structures and Research of Magnetic Properties

Abstract

By the solvothermal reactions of a [1,1′:3′,1″-terphenyl]-3,3″,5,5″-tetracarboxylic acid (H4tpta) with transition metal ions, three novel polymeric complexes, namely {[Ni2(tpta)(H2O)3]·H2O}n (1), {[Co4(tpta)2(4,4′-bpy)(H2O)3]·3H2O}n (2), and {[Mn2(tpta)(H2O)2]·2H2O}n (3), have been isolated. The heterometallic clusters of these polymeric complexes are dimeric and tetrameric, respectively. 1 is composed of dimeric paddle wheel Ni(II) units to generate a 2D structure. In complexes 2 and 3, metal ions form tetrameric units that extend via all dimensions to give 3D structures with the Schläfli symbol of (43)(43)(46·618·84) and (46)(412·53·69·74), respectively. The results of variable temperature magnetization measurements (χmT-T and χm–1-T) show that complexes 1 and 2 display unusual ferromagnetic coupling via the M–O–C–O–M bridges, while complex 3 shows predominantly antiferromagnetic behavior. The M(H) curve of 1 does not saturate until the highest field of 80 kOe, indicating the significant magnetic anisotropy in this complex system, whereas the final saturation value of 2.79 Nβ for 2 manifests the existence of typically paramagnetic property and the absence of long-range magnetic ordering. The dynamic magnetization experiments have been also carried out to further explore the magnetic behaviors of 1 and 2. There are no frequency dependences in the dynamic magnetization experiments, suggesting the absence of slow magnetic relaxation of these two complexes.