Diaqua­tris­(nitrato-κ(2) O,O′){2,2′-[pyridine-2,6-diylbis(methyl­ene­oxy)]dibenzaldehyde-κO (1)}dysprosium(III)–2,2′-[pyridine-2,6-diylbis(methyl­ene­oxy)]dibenzaldehyde (1/1)

The title compound, [Dy(NO(3))(3)(C(21)H(17)NO(4))(H(2)O)(2)]·C(21)H(17)NO(4), may be considered as an organic–metalorganic 1:1 co-crystal, in which the two dialdehyde mol­ecules act as a ligand and as an organic moiety, respectively. The Dy(III) atom coordinates nine O atoms from the organic ligand, bidentate nitrate ions and water mol­ecules, approximating a square-face-tricapped trigonal–prismatic geometry. The coordinated dialdehyde is not planar: the uncoordinated oxybenzaldehyde group is twisted by 39.96 (4)° from the rest of the ligand. In contrast, the free organic moiety is almost planar, with an r.m.s. deviation of 0.15 Å. In the crystal, segregated stacks of dialdehyde are formed in the [100] direction. For the complex, the shortest π–π contact is found at 3.781 (2) Å, and for the free ligand, at 3.785 (2) Å. The crystal structure is further stabilized by O—H⋯O and O—H⋯N hydrogen bonds in which coordinated water mol­ecules are the donor groups.