Poly[[tetra-aqua-(μ(4)-imidazole-4,5-dicarboxyl-ato)(μ(3)-imidazole-4,5-dicarboxyl-ato)-μ(3)-sulfato-μ(2)-sulfato-cobalt(II)digadolinium(III)] monohydrate].

The asymmetric unit of the title compound, {[CoGd2(C5H2N2O4)2(SO4)2(H2O)4]·H2O}n, contains one CoII ion, two GdIII ions, two imidazole-4,5-dicarboxyl­ate ligands, two SO4 2− anions, four coordinated water mol­ecules and one uncoordinated water mol­ecule. The CoII ion is six-coordinated by two O atoms from two coordinated water mol­ecules, as well as two O atoms and two N atoms from two imidazole-4,5-dicarboxyl­ate ligands, giving a slightly distorted octa­hedral geometry. Both GdIII ions are eight-coordinated in a distorted bicapped trigonal–prismatic geometry. One GdIII ion is coordinated by four O atoms from two imidazole-4,5-dicarboxyl­ate ligands, three O atoms from three SO4 2− anions and a water O atom; the other GdIII ion is bonded to five O atoms from three imidazole-4,5-dicarboxyl­ate ligands, two O atoms from two SO4 2− anions as well as a water O atom. These metal coordination units are connected by bridging imidazole-4,5-dicarboxyl­ate and sulfate ligands, generating a heterometallic layer parallel to the ac plane. The layers are stacked along the b axis via N—HO, O—HO, and C—HO hydrogen-bonding inter­actions, generating a three-dimensional framework.