A novel Cu-Na heteronuclear three-dimensional coordination polymer, poly[diaquadi-μ5-iminodiacetato-di-μ4-iminodiacetato-tricopper(II)disodium(I)], [Cu3Na2(C4H5NO4)4(H2O)2]n, has been prepared by hydrothermal synthesis. The asymmetric unit contains one and a half copper(II) cations, a sodium cation, two iminodiacetate (ida) ligands and a coordinated water ligand. One of the two independent Cu(II) centres is in a general position and is five-coordinated in a distorted square-pyramidal geometry. A [Cu(ida)] unit is formed via a bis-chelating ida ligand and the coordination sphere of the Cu(II) atom is completed by two O atoms of two different neighbouring [Cu(ida)2] units. These [Cu(ida)2] units are associated with the second Cu(II) cation, which is located on a crystallographic inversion centre and is coordinated in a distorted square-planar geometry by two chelating ida ligands. The carboxylate groups of the ida ligands act as bridges and connect the [Cu(ida)] and [Cu(ida)2] building blocks in a 2:1 ratio, forming two-dimensional arrays. These layers are interconnected into a three-dimensional structure by the sodium ions. Each Na(I) cation is coordinated by six O atoms from five ida ligands and a water molecule. When [Cu(ida)], the Na(I) cations and [Cu(ida)2] are viewed as 5-, 5- and 8-connected nodes, respectively, the three-dimensional network exhibits a (3(2).4(3).5(2).6(3))2(3(2).4(3).5(2).6(3))2(3(4).6(16).7(8)) topology.