catena-Poly[[[tetra­aqua­erbium(III)]-μ-oxalato-κ(4) O (1),O (2):O (1′),O (2′)] [bromidobis(pyrazine-2-carboxyl­ato-κ(2) N (1),O)cuprate(II)] tetra­hydrate]

In the title heterometallic complex, {[Er(C(2)O(4))(H(2)O)(4)][CuBr(C(5)H(3)N(2)O(2))(2)]·4H(2)O}(n), the Er(III) atom is eight-coordin­ated by four O atoms from two centrosymmetric oxalate ligands and four water mol­ecules, displaying a bicapped trigonal-prismatic geometry. The oxalate ligands bridge the Er atoms into a polymeric cationic chain along [110]. The Cu(II) atom is five-coordinated in a square-pyramidal geometry by two pyrazine-2-carboxyl­ate ligands and a Br atom, forming a discrete anion. The polymeric cations, complex anions and uncoordinated water mol­ecules are self-assembled into a three-dimensional supra­molecular network through O—H⋯N, O—H⋯O and O—H⋯Br hydrogen bonds.