Structure, magnetic, and electrochemical properties of complexes of 3d-metals as redox-active units for assembling coordination polymers and porous coordination polymer on their basis

Mononuclear complexes ML2 (M-II = Fe, Co, Cu, Zn) and porous coordination polymer [{Fe2NiO(Piv)(6)}{CoL2}(1.5)] (n) (LH is the Schiff base of pyridine-4-carboxylic acid hydrazide and pyridine-2-carbaldehyde, and Piv(-) is pivalate) were synthesized and characterized. The structures of the compounds were determined by X-ray diffraction analyses. Each ML2 molecule contains two 4-pyridine fragments capable of coordinating metal ions. Polymer [{Fe2NiO(Piv)(6)}{CoL2}(1.5)] (n) was formed by cross-linking of trinuclear units with the CoL2 bridge. The temperature dependences of the magnetic susceptibility of CoL2, FeL2, and [{Fe2NiO(Piv)(6)}{CoL2}(1.5)] (n) were studied. The magnetic properties of [{Fe2NiO(Piv)(6)}{CoL2}(1.5)] (n) were described as a superposition of the susceptibilites of the trinuclear and mononuclear units, and their interaction was taken into account in the framework of the molecular field model. The magnetic properties of CoL2 in the individual state and in the framework of [{Fe2NiO(Piv)(6)}{CoL2}(1.5)] (n) were interpreted using a model taking into account the spin-orbit coupling in the Co2+ ion and the splitting of its levels by crystal field. For FeL2, a model taking into account the zero-field splitting of the ground state of the Fe2+ ion was used. Several redox processes were found for ML2 in a solution and for [{Fe2NiO(Piv)(6)}{CoL2}(1.5)] (n) in a suspension by cyclic voltammetry. The CoL2 and FeL2 complexes can catalyze the electrochemical dehalogenation of freon CF2ClCFCl2 but exhibit no activity in the dehalogenation of CHCl3; ZnL2 did not show catalytic activity in the dehalogenation of both substrates.