A Linear Trinuclear Acetate Bridged Cobalt Complex Containing Pyridine-Based Bicompartmental Ligand: Synthesis, Structural, Magnetic, and Electrocatalytic Oxygen Evolution Studies

Abstract

The reaction of Co(OAc)(2)<middle dot>4H(2)O, LH2, and Et3N in a 1.5:1:3 molar ratio affords a linear trinuclear complex, [Co-3(L)(2)(mu-eta(1): eta(1)-OAc)(2)(CH3CN)(2)] (<bold>1</bold>). The synthesized complex was characterized by single crystal X-ray diffraction studies, and it exhibited better electrocatalytic activity for the oxygen evolution reaction (OER) compared with the catalyst, RuO2. The complex exhibits an overpotential of 380 mV at 10 mA cm(-2) current density for the OER, which is better than that of RuO2 (480 mV) under identical experimental conditions. The Tafel slope values of the complex and RuO2 were calculated to determine the kinetics of the electrochemical reaction and were found to be 58 and 85 mV/dec, respectively, which implies its robust heterogeneous OER catalysis. The DC magnetic studies revealed that the coupling between the Co(II) ions through the dioxo bridges was found to be antiferromagnetic, and the best-fit yielded exchange interaction J = -3.077(3) cm(-1), zero field splitting parameters D-1 = 46.35(6) cm(-1) and D-2 = 5.831(7) cm(-1), g = 2.56(2), theta = 90.3(1) degrees, and sigma(chi T) = 2.4 x 10(-5). The positive values of D-2 are consistent with the orbital singlet ground term (4)A(2g) in the octahedral coordination, which suggest that the central and terminal Co(II) ions show easy-plane anisotropies.

The reaction of Co(OAc)2·4H2O, LH2, and Et3N in a 1.5:1:3 molar ratio affords a linear trinuclear complex, [Co3(L)2(μ-η1: η1-OAc)2(CH3CN)2] (1). The synthesized complex was characterized by single crystal X-ray diffraction studies, and it exhibited better electrocatalytic activity for the oxygen evolution reaction (OER) compared with the catalyst, RuO2. The complex exhibits an overpotential of 380 mV at 10 mA cm-2 current density for the OER, which is better than that of RuO2 (480 mV) under identical experimental conditions. The Tafel slope values of the complex and RuO2 were calculated to determine the kinetics of the electrochemical reaction and were found to be 58 and 85 mV/dec, respectively, which implies its robust heterogeneous OER catalysis. The DC magnetic studies revealed that the coupling between the Co(II) ions through the dioxo bridges was found to be antiferromagnetic, and the best-fit yielded exchange interaction J = −3.077(3) cm-1, zero field splitting parameters D1 = 46.35(6) cm-1 and D2 = 5.831(7) cm-1, g = 2.56(2), θ = 90.3(1) °, and σχT = 2.4 × 10-5. The positive values of D2 are consistent with the orbital singlet ground term 4A2g in the octahedral coordination, which suggest that the central and terminal Co(II) ions show easy-plane anisotropies.