Two Co^II Metal–Organic Frameworks Based on a Multicarboxylate Ligand as Electrocatalysts for Water Splitting

Abstract

By using a rigid multicarboxylate ligand, 4,5-di(4'-carboxylphenyl)phthalic acid (H₄ L), two Co^II complexes formulated as [Co₄ L₂ (4,4'-bpy)(H₂ O)₆ ]⋅3.5 H₂ O (4,4'-bpy=4,4'-bipyridine) (1) and [Co₂ L(azene)(H₂ O)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 L^4- 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.