The homodinuclear CoII helicate complex [CoII(DQPD)]2 (1) was prepared by treating [Co­(H2O)6]­(ClO4)2 with the deprotonated form of the ligand N 2,N 6-bis­(quinolin-8-yl)­pyridine-2,6-dicarboxamide (DQPDH2). Complex 1 represents a discrete homodinuclear helicate complex with two CoII centers having a distorted-octahedral geometry through an unprecedented pyridine bridge. Complex 1, upon treatment with H2O2, undergoes oxidation at one of the CoII centers followed by a structural deformation to generate the mixed-valence complex [CoIIICoII(DQPD)2]­(ClO4) (2·ClO 4 ). In complex 2, the bridging through the central pyridine collapses along with the formation of Co­(III) octahedral and Co­(II) tetrahedral environments. Complexes 1 and 2 interconvert to one another. The effective magnetic moments for complexes 1 and 2 are respectively 5.88 and 4.30 μB. Complexes 1 and 2 have been employed for electrocatalytic proton reduction using AcOH as the proton source in 95/5 (v/v) DMF/H2O. A TOF of 30000 mmol of H2 h–1 (mol of 1)−1 at a potential of −1.7 V vs SCE was achieved. A resting-state analysis has been carried out to support the mechanism for the catalytic proton reduction.

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Catalytic CO 2 reduction is an emerging domain of sustainable energy. The behavior of polypyridyl ligand to reduce CO 2 into value-added products is quite rare. In this study, the Fc-NAP 2 (Fc-NAP 2 = 1,1-bis[1,8-naphthyrid-2-yl]ferrocene) has been employed for CO 2 reduction in CH 3 CN/H 2 O (90 : 10, v/v) under homogeneous electrochemical conditions at À 1.6 V vs. SCE. The Fc-NAP 2 efficiently produces CO/HCOOH/H 2 from CO 2 through proton coupled 2e À reduction at an overpotential of 735 mV vs. SCE, wherein the TOF and Faradaic efficiency of CO, H 2 , and HCOOH was found to be 8.5 h À 1 , 14 h À 1 , 4.61 h À 1 and 11.9 � 0.09 %, 19.4 � 0.08 %, 10.8 � 0.02 % respectively at À 1.6 V vs. SCE after 3 h of electrolysis.