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 ML 2 (M II = Fe, Co, Cu, Zn) and porous coordination polymer [{Fe 2 NiO(Piv) 6 }{CoL 2 } 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 ML 2 molecule contains two 4-pyridine fragments capable of coordinating metal ions. Polymer [{Fe 2 NiO(Piv) 6 }{CoL 2 } 1.5 ] n was formed by cross-linking of trinuclear units with the CoL 2 bridge. The temperature dependences of the magnetic susceptibility of CoL 2 , FeL 2 , and [{Fe 2 NiO(Piv) 6 }{CoL 2 } 1.5 ] n were studied. The magnetic properties of [{Fe 2 NiO(Piv) 6 }{CoL 2 } 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 CoL 2 in the individual state and in the framework of [{Fe 2 NiO(Piv) 6 }{CoL 2 } 1.5 ] n were interpreted using a model taking into account the spin—orbit coupling in the Co 2+ ion and the splitting of its levels by crystal field. For FeL 2 , a model taking into account the zero-field splitting of the ground state of the Fe 2+ ion was used. Several redox processes were found for ML 2 in a solution and for [{Fe 2 NiO(Piv) 6 }{CoL 2 } 1.5 ] n in a suspension by cyclic voltammetry. The CoL 2 and FeL 2 complexes can catalyze the electrochemical dehalogenation of freon CF 2 ClCFCl 2 but exhibit no activity in the dehalogenation of CHCl 3 ; ZnL 2 did not show catalytic activity in the dehalogenation of both substrates.