The coordination of benzene-1,3,5-tribenzoate (BTB) and imidazole (Im) with cobalt under basic conditions yields a 2D layered structure, Co 3 (BTB) 1.5 (Im) 1.35 (O) 0.5 (OH) 0.5 (H 2 O) 1.65 guests (1), in which the imidazoles are weakly π–π stacked and hydrogen bonded to the adjacent layers affording a 3D supramolecular network. The structure is based on a hexanuclear Co 6 building unit which comprises four octahedral and two tetrahedral Co(II) centres. The framework is permanently porous to N 2 , CO 2 and CH 4 , with the strength of interaction at zero coverage being comparable to that at high loading.