1,10-Phenanthrolin-1-ium nitrate–aqua­bis­(4-hydroxy­benzoato-κ(2) O,O′)(nitrato-κ(2) O,O′)(1,10-phenanthroline-κ(2) N,N′)erbium(III)–1,10-phenanthroline–water (1/1/0.5/2)

In the title compound, C(12)H(9)N(2) (+)·NO(3) (−)·[Er(C(7)H(5)O(3))(2)(NO(3))(C(12)H(8)N(2))(H(2)O)]·0.5C(12)H(8)N(2)·2H(2)O, the water-mol­ecule-coordinated Er(III) ion is chelated by one 1,10-phenanthroline (phen) ligand, two 4-hy­droxy­benzoate anions and one nitrate anion in a monocapped square-anti­prismatic coordination geometry. The uncoordinating phen mol­ecule is approximately parallel to the 1,10-phenanthrolin-1-ium (Hphen) anion [dihedral angle = 3.3 (4)°]. The centroid–centroid distance of 3.801 (5) Å between pyridine rings suggests the existence of π–π stacking. The crystal structure contains an extensive network of classical O—H⋯O and N—H⋯O and weak C—H⋯O hydrogen bonds. C—H⋯π inter­actions between phen and 4-hy­droxy­benzoate is also present in the crystal structure. In the crystal, the uncoordinating phen is equally disordered over two sites about an inversion center.