Effect of the Structure of Pyridine Ligands and the Substituent in the Carboxylate Anion on the Geometry of Transition Metal Complexes [M2(O2CR)4L2]

Resumo

A series of binuclear tetracarboxylate-linked Mn(II), Fe(II), Co(II), Ni(II), and Cu(II) complexes with 1,2-substituted pyridine, viz., 2,3-cyclododecenopyridine (L), were prepared. Study of the crystal structures of isolated compounds (CIF file CCDC nos. 1575855–1575859) revealed a distortion of the {Ni₂(O₂CR)₄L₂} binuclear moiety, manifested as a change in the NiNiN angle (151.67°), in the bridging function of two out of the four carboxylate groups (from μ_2- to (κ²,μ_2-)), and in the coordination environment of the metal ion (NiO₅N). The results were analyzed in comparison with known data. The magnetic properties of copper(II) and nickel(II) complexes were studied. The copper(II) complex is diamagnetic as a result of strong exchange interactions between the unpaired electrons; in the nickel(II) complex antiferromagnetic exchange interactions were detected (J_Ni–Ni =–25 cm^–1).