A layered aluminium carboxylate containing the 4,4′-azobenzenedicarboxylate anion (MIL-129) has been hydrothermally synthesized (210 °C, 24 h). Its crystal structure was determined by means of microdiffraction technique using synchrotron radiation. It consists of infinite trans-connected chains of aluminium-centered octahedra, linked to each other through the organic molecules, in order to generate infinite sheets, containing double stacking of organic species. The cohesion of the structure is ensured by the close packing due to π–π interactions between aromatic rings of the ligands and no porosity is observed.