[{Cu(phen)2}(mu-malato){Cu(phen)(NO3)}](NO3).4H2O: malate acting as a tetradentate and dibridging ligand in a dinuclear copper complex.

The crystal structure of the title compound, mu-2-hydroxybutanedioato-1kappa2O4,O4':2kappa3O1,O2,O4-nitrato-2kappaO-tris(1,10-phenanthroline)-1kappa(4)N,N';2kappa(2)N,N'-dicopper(II) nitrate tetrahydrate, Cu2(C4H3O5)(NO3)(C12H8N2)3.4H2O, contains an unsymmetrical dinuclear copper complex with Cu(phen)2 and Cu(phen)(NO3) moieties (phen is 1,10-phenanthroline) bridged by a malate (2-hydroxybutanedioate) ligand, which acts as a double-bridging and tetradentate ligand. As a result of this double-bridging action, especially the direct coordination of the O atom of one carboxylate group of malate to the two Cu atoms, the Cu...Cu distance is only 4.199 (1) Angstrom and the two phen planes are roughly parallel [the shortest interplanar distance is 3.28 (1) Angstrom], exhibiting an obvious intramolecular pi-pi stacking interaction.