Bis(5-hy-droxy-isophthalato-κO (1))bis-[4-(pyridine-3-carboxamido-κN (3))pyridinium]copper(II) tetra-hydrate.

In the title compound, [Cu(C11H10N3O)2(C8H4O5)2]·4H2O, the Cu(II) ion, located on a crystallographic inversion center, is coordinated in a square-planar environment by two trans-O atoms belonging to two monodentate 5-hy-droxy-isophthalate (hip) dianions and two trans nicotinamide pyridyl N-donor atoms from monodentate protonated pendant N-(pyridin-4-yl)nicotinamide (4-pnaH) ligands. The protonated 4-pyridyl-amine groups engage in N-H(+)⋯O(-) hydrogen-bond donation to unligated hip O atoms to construct supra-molecular chain motifs parallel to [100]. Water mol-ecules of crystallization, situated between the chains, engage in O-H⋯O hydrogen bonding to form supra-molecular layers and the overall three-dimensional network structure.