Herein we report the structure and adsorption behaviour of a new MOF, PCN-53 (PCN stands for porous coordination network), which is composed of benzo-tris-thiophene carboxylate (BTTC) linkers and Fe 3 O nodes. The structure of PCN-53 is unusual among MOFs. Each of the metal cluster nodes has three coordinatively unsaturated Fe sites, two of which are trivalent and the other is divalent. In addition, the structure contains both micro- and meso-pores, ...