Pyridyldicarboxamide-based multinuclear complexes: Syntheses, structural characterizations, and magnetic properties

Using the pyridine dicarboxamide derivative N,N′-bis(1,3,4-thiadiazol-2-yl)-2,6-pyridinedi-carboxamide (H₂-btapca) as ligand, two novel polynuclear complexes: dimeric {Cu₂(μ₂-O₂H)(btapca)₂]·DMF·H₂O} (1) and tetrameric {Ni₄((μ₂-O₂H)₂(btapca)₄)]·DMF·MeOH·3.5H₂O} (2) were obtained. In complex 1, two center Cu(II) ions are bounded by two btapca ligands and one aqueous molecule acting as a μ₂-H₂O bridge connect them together. Complex 2 is a tetrameric complex, in which the based backbone is an assumed Ni₄ tetrahedron with two μ₂-O₂H bridges existing inside the tetrahedron forming a basic Ni₂(μ₂-O₂H)]₂ core, which are surrounded by four btapca ligands. The magnetic properties of the two polynuclear complexes were determined, the results show that for both of the two complexes, the overall weak ferromagnetic exchange interactions between central metal ions are evident, the best fitting parameters are: J = 7.47 cm⁻¹ (g = 2.21) for dimeric Cu(II) complex 1, and 2J₁ = 4.8 cm⁻¹, 2J₂ = −0.00204 cm⁻¹(g = 2.14, zJ′ = 0.00077 cm⁻¹) for tetrameric Ni(II) complex 2.