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

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.