This paper reports the synthesis and crystal structure of a novel mixed valence copper(I,II) compound, (Cu2CuII)-Cu-I(hedpH(2))(2)(4,4'-bpy)(2).2H(2)O (1), where hedp represents 1-hydroxyethylidenediphosphonate. The structure is composed of {(Cu2CuII)-Cu-I(hedpH(2))(2)} trimer units and 4,4'-bipyridine linkages, forming a two-dimensional brick-wall-like layer structure in the ab plane. The layers are stacked along the [001] direction with strong interlayer hydrogen bonds and pi-pi interactions, thus leading to the construction of a three-dimensional network.