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

Abstract

International audienceMononuclear complexes ML2 (MII = 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 substrate

Modeling of catalytically active metal complex species and intermediates in reactions of organic halides electroreduction

“…As we previously showed, 18,19 M(L1) 2 complexes exhibited electrocatalytic activity in dehalogenation reactions of organic halides, as can be concluded from the increase in cathodic It was found that the electrocatalytic activity of Co(L1) 2 and Fe(L1) 2 was quite moderate: an increase in R113 concentration led to current saturation at about a 50% increase. 19 However, the reduction of CHCl 3 was not catalyzed by Co or Fe complexes.…”

“…As we reported, 18,19 the complex species M(L1) 2 (M II = Co, Ni, Fe) showed electrocatalytic activity in reductive electrochemical dehalogenation of organic halides. In particular, Ni(L1) 2 catalyzed the dehalogenation of CHCl 19 The process [M(L1) 2 ] 0 /[M(L1) 2 ] À was responsible for the catalytic activity in dehalogenation. In order to find out where the additional electron is localized in [M(L1) 2 ] À ions (i.e.…”

“…This dependence agrees with the above-mentioned results of detailed modeling of the [Ni(L1) 2 ] À and [Co(L1) 2 ] À species: a lower spin-down LUMO energy in respect to the spinup energy favors the low-spin state of the reduced form. The energies of the spin-down LUMO correlate with the E 1/2 potentials of [M(L1) 2 ] 0 /[M(L1) 2 ] À (Table 4) 19 and the spin-down LUMO population on the metal atom (a lower spin-down LUMO energy is associated with an increase in E 1/2 and a more localized character of the orbital, see also Fig. 3).…”

“…Notably, the ligand L1H was also redox-active, and exhibited an irreversible reduction at E c = À2.16 V vs. the Fc + /Fc couple. 19 Although the X-ray molecular structure of the neutral [Ni(L1) 2 ] 0 molecule was determined and [Co(L1) 2 ] 0 was shown to be isostructural, geometry optimization of these species using the DFT method with exchange-correlation potential TPSS was carried out in order to obtain the geometries of these molecules taking solvation effects into account (details are presented in the Experimental section).…”

“…1). 18,19 It was also shown that the electrochemical activity of M(L1) 2 (M = Ni, Co) was preserved upon incorporation of these species as bridging units into porous coordination polymers {Fe 2 M 0 O(Piv) 6 }{M(L1) 2 } 1.5 (M = Ni II , M 0 = Co II ; M = Co II , M 0 = Ni II ).…”