Na[Cu(O3P-(CH2)(2)-CO2)], or MIL-39 (for Material of Institut Lavoisier), was synthesized hydrothermally at 443 K for 72 h under autogenous pressure. Its three-dimensional open structure was determined from X-ray powder diffraction. MIL-39 is monoclinic, it crystallizes in the space group P2(1)/m, (No. 11) with the following cell parameters at 293 K: a = 8.808(1) Angstrom, b = 6.4149(8) Angstrom, c = 5.3418(8) Angstrom, beta = 105.75(1)degrees, Z = 2. Its framework contains double rows built from isolated distorted CuO5 square pyramids linked by PO3C tetrahedral groups from (O3P-(CH2)(2)-CO2)(3-) organic moieties. At the other end of these latter moieties, the carboxylate group links two different Cu polyhedra of two neighboring chains. These connections define two types of channels along [010].