Na 2 Zn{O 3 P CH 2 PO 3 }.H 2 O (labelled MIL-58) was hydrothermally synthesized at 443 K in the quaternary system ZnCl 2 :H 2 O 3 P CH 2 PO 3 H 2 :NaOH:H 2 O. Its orthorhombic structure was solved from single crystals X-ray diffraction data in the non-centrosymmetric P2 1 2 1 2 1 (No. 19) space group with lattice parameters a=8.3215(7), b=9.3276(8), c=9.6958(8) Å, V=752.6(1) Å 3 , Z=4, R 1 (F o )=0.0582, wR 2 (F o 2 )=0.1256 for 1945 reflections I>=2σ(I). Its three-dimensional structure is built up from corner-shared trimers containing one ZnO 4 tetrahedron chelated by one methylenediphosphonate unit. The connections between the trimers generate eight-membered channels where the Na + cations and the water molecules are located.