Co‐crystallization of hemimellitic acid with 4,4′‐bipyridine forming a pillar‐layered hydrogen‐bonded network

Co‐crystallization of hemimellitic acid (benzene‐1,2,3‐tricarboxylic acid) dihydrate (H₃HMA·2H₂O) with 4,4′‐bipyridine (4,4′‐bpy) affords the 1:1 co‐crystal benzene‐1,2,3‐tricarboxylic acid–4,4′‐bipyridine (1/1), H₃HMA·4,4′‐bpy or C₉H₆O₆·C₁₀H₈N₂. Strong O—H⋯O hydrogen bonds connect the acid mol­ecules to form a one‐dimensional zigzag chain, around which the 4,4′‐bpy components are fixed as arms via O—H⋯N inter­actions, resulting in a ladder motif. Through weak C—H⋯O non‐covalent forces, the resulting acid layers are extended into a three‐dimensional pillar‐layered architecture supported by rod‐like 4,4′‐bpy components. The influence on hydrogen‐bonding models is also discussed, with the discovery of an unexpected inter­action motif that does not follow the routine hydrogen‐bonded hierarchical rule in the construction of an acid–base co‐crystal.