Poly[[aqua-bis(μ(3)-isonicotinato-κO:O':N)tris-(μ(2)-isonicotinato-κO,O':N)(nitrato-κO)bis-(μ(4)-oxalato-κO,O:O:O,O:O)dierbium(III)tetra-silver(I)] tetra-hydrate].

In the title coordination polymer, {[Ag(4)Er(2)(C(6)H(4)NO(2))(5)(C(2)O(4))(2)(NO(3))(H(2)O)]·4H(2)O}(n), each Er(III) atom is coordinated in a bicapped trigonal-prismatic coordination geometry by three O atoms from two isonicotinate (IN) ligands, four O atoms from two oxalate ligands and one O atom from either a nitrate ion or a water mol-ecule, both of which are half-occupied over the same site. One Ag(I) atom has a Y-shaped geometry defined by one N atom from one IN ligand, one O atom from another IN ligand and one O atom from an oxalate ligand. The other Ag(I) atom is coordinated by two IN ligands and one O atom from an oxalate ligand. One of the IN ligands is disordered over an inversion center and forms a bridge between two centrosymmetric Ag(I) ions. Due to the disorder, this IN ligand coordinates to the Ag atom through either the pyridyl N or the carboxyl-ate O atoms. The IN and oxalate ligands link the Er and Ag atoms into a three-dimensional coordination framework. O-H⋯O and C-H⋯O hydrogen bonds are observed in the crystal structure.