Redox-Induced Structural Switching through Sporadic Pyridine-Bridged CoCo Dimer and Electrocatalytic Proton Reduction.

The homodinuclear Co helicate complex [Co(DQPD)] () was prepared by treating Co(HO) with the deprotonated form of the ligand ,-bis(quinolin-8-yl)pyridine-2,6-dicarboxamide (DQPDH). Complex represents a discrete homodinuclear helicate complex with two Co centers having a distorted-octahedral geometry through an unprecedented pyridine bridge. Complex , upon treatment with HO, undergoes oxidation at one of the Co centers followed by a structural deformation to generate the mixed-valence complex CoCo(DQPD) (). In complex , the bridging through the central pyridine collapses along with the formation of Co(III) octahedral and Co(II) tetrahedral environments. Complexes and interconvert to one another. The effective magnetic moments for complexes and are respectively 5.88 and 4.30 μ. Complexes and have been employed for electrocatalytic proton reduction using AcOH as the proton source in 95/5 (v/v) DMF/HO. A TOF of 30000 mmol of H h (mol of ) 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.