Tetra-kis(μ-6-hydr-oxy-1-naphthoato)bis-[(6-hydr-oxy-1-naphthoato)(1,10-phenanthroline)europium(III)] dihydrate.

The title complex, [Eu(2)(C(11)H(7)O(3))(6)(C(12)H(8)N(2))(2)]·2H(2)O, has a centrosymmetric binuclear cage structure in which the two Eu(III) ions are both nine-coordinated and bridged by 6-hy-droxy-1-naphthoate (L) ligands, with an Eu⋯ Eu separation of 4.1594 (4) Å. The remaining coordination sites are occupied by two N atoms from one 1,10-phenanthroline (phen) and two O atoms from an L ligand. The six 6-hydr-oxy-1-naphthoate groups coordinate each Eu(III) atom in three different ways, namely μ(2)-η(1):η(1)-bridging, μ(1)-η(1):η(1)-chelating, and μ(2)-η(1):η(2)-chelating/bridging modes. Adjacent discrete dinuclear units are linked into a two-dimensional sheet parallel to (011) by inter-molecular O-H⋯O hydrogen-bonding inter-actions. The sheets are cross-linked by water mol-ecules, forming a three-dimensional network. In addition, π-π stacking inter-actions, with a centroid-centroid separation of 3.547 (2) Å are observed.