Two CoII Metal–Organic Frameworks Based on a Multicarboxylate Ligand as Electrocatalysts for Water Splitting

By using a rigid multicarboxylate ligand, 4,5-di(4′-carboxylphenyl)phthalic acid (H4L), two CoII complexes formulated as [Co4L2(4,4′-bpy)(H2O)6]⋅3.5 H2O (4,4′-bpy=4,4′-bipyridine) (1) and [Co2L(azene)(H2O)3]⋅DMF (azene=(E)-1,2-di(pyridin-4-yl)diazene, DMF=dimethylformamide) (2) have been synthesized and structurally characterized by single-crystal X-ray diffraction. Complex 1 features a novel three-nodal (4,5,6)-connected 2 D framework with an unusual (32.42.5.63.7.8)(32.42.5.6)(32.46.52.64.7) topology. Complex 2 exhibits a novel two-nodal (4,7)-connected 3 D framework with an unusual (43.5.62)(45.55.69.7.8) topology. Ligand L4− displays different coordination modes in the two complexes. The complexes both exhibit electrocatalytic activities toward generating H2 and O2 from water with lowered overpotentials and enhanced currents. The different electrocatalytic properties of the two complexes are related to their different ligands and frameworks.