MIL-12, formulated Al 2 (PO 4 )(OH x , F 5−x )N 2 C 3 H 12 , with x≈2, is a new layered fluoroaluminophosphate formed at the early stages of ULM-4 by hydrothermal synthesis using 1-3, Diaminopropane as a template (Al(OH) 3 /H 3 PO 4 /HF/1-3 DAP/H 2 O:ratio 1 : 1 : 3 : 0.5 : 80, 180°C/2 days). It crystallises in the monoclinic space group P2 1 /m with a=11.072(1) Å, b=7.012 (2) Å, c=6.1096 (8) Å, β=100.98 (1)° and Z=2. Its structure was solved ab initio from conventional X-ray powder diffraction data and refined by the Rietveld method with satisfactory crystal-structure model indicators (R B =0.088 and R F =0.062) and profile factors (R wp =0.124 and R p =0.161). It consists of [Al 2 (PO 4 )(OH, F) −2 5 ] macroanionic sheets perpendicular to the a axis in which OH − and F − ions are statistically distributed. Aluminum octahedra are linked together to form zig-zag chains running parallel to the b axis; the phosphate groups ensure the connection of the aluminum chains within the (100) layer. Protonated 1-3, Diaminopropane is interleaved between the sheets and ensures the cohesion of the structure by hydrogen bonds. Structural relations with other solids built with the same type of chains are presented.