Metal( ii ) complexes based on 4-(2,6-di(pyridin-4-yl)pyridin-4-yl)benzonitrile: structures and electrocatalysis in hydrogen evolution reaction from water

Using a novel rigid ditopic ligand, 4-(2,6-di(pyridin-4-yl)pyridin-4-yl)benzonitrile ( L ), three metal( ii ) complexes formulated as M 2 L 2 (SO 4 ) 2 (H 2 O) 6 ·H 2 O (M = Ni ( 1 ), Co ( 2 ) and Cd ( 3 )) have been solvothermally synthesized and structurally characterized by single-crystal X-ray diffraction. The three complexes are isostructural except for the different metal( ii ) ions in the structures. They all show a one-dimensional (1D) chain, in which the L ligand acts as a μ 2 -bridge linking two metal( ii ) centers. Different chains are connected by strong H bonds and π–π stacking interactions into a three-dimensional (3D) supramolecular architecture. Among the three complexes, the Ni complex 1 and the Co complex 2 can act as the electrocatalysts for the hydrogen evolution reaction (HER) from water, and the Co complex 2 shows better electrocatalytic activity. In the present work, the graphene cannot catalyze the HER; however, the complex 1 /graphene composite shows similar electrocatalytic activity to complex 1 . The three complexes show different UV-vis absorption values, photoluminescence properties and thermal stabilities.