An Experimental

R factor = 0.046; wR factor = 0.075; data-to-parameter ratio = 12.3. In the structure of the title salt, [Rb2(C7H5N2O4)2(H2O)2]n, the asymmetric unit comprises two independent and different seven-coordinate Rb+ cations, one forming an RbO7 poly-hedron, the other a RbO6N polyhedron, each of which is considerably distorted. The RbO7 polyhedron comprises bridging O-atom donors from two water molecules, three carboxylate groups, and two nitro groups. The RbO6N polyhedron comprises the two bridging water molecules, one monodentate amine N-atom donor, one carboxyl O-atom donor and three O-atom donors from nitro groups (one from the chelate bridge). The extension of the dinuclear unit gives a three-dimensional polymeric structure which is stabilized by both intra- and intermolecular amine N—H O and water O—H O hydrogen bonds to carboxyl and water O-atom acceptors, as well as a number of inter-ring – interactions [minimum centroid–centroid separation = 3.364 (2) Å]. The title salt is isostructural with the analogous caesium salt. Related literature For the structures of some rubidium salts of substitute