The (bis aqua)(sebacato)magnesium Mg((κ 2 )-(κ 1 -κ 1 )-μ 3 -C 10 H 16 O 4 )(H 2 O) 2 was synthesized by hydrothermal route. The structure was solved ab initio using optimisation methods from powder X-ray diffraction (PXRD) laboratory data. The structure crystallises in the monoclinic space group P2 1 /c with a = 17.336(1) Å, b = 7.456(1) Å, c = 9.573(1) Å, β = 96.43 (1) °, V = 1229.61(9) Å 3 , Dx = 1.407 g cm −3 and Z = 4. Rietveld refinement from 399 reflexions leads to a reliability factor R bragg = 0.06. The structure consists of double sheets of Mg 2+ centred O-octahedra linked by H-bonds and bridged by sebacate anions along [100], building a 3D metal-organic framework ‘MOF’. Heating at 100 °C provokes the condensation of the octahedra in an anhydrous compound Mg(C 10 H 16 O 4 ).