A new supra-molecular cobalt(II) complex based on 1,10-phenanthroline and 4-nitro-phthalate ligands.

The title compound, bis-(μ-2-carb-oxy-4-nitro-benzoato-κ2 O 1:O 1')bis-[bis-(1,10-phenanthroline-κ2 N,N')cobalt(II)] bis-(2-carb-oxy-4-nitro-benzoate) tetra-hydrate, [Co2(C8H4NO6)2(C12H8N2)4](C8H4NO6)2·4H2O, comprises a centrosymmetric dinuclear cobalt(II) complex dication, two hydrogen 4-nitro-phthalate anions and four water mol-ecules of crystallization. The two CoII atoms are linked by two μ-hydrogen 4-nitro-phthalato ligands, generating a centrosymmetric dinuclear unit. Each cobalt(II) centre adopts a distorted octa-hedral coordination geometry defined by four N atoms from two chelating 1,10-phenanthroline ligands and two O atoms from two symmetry-related bridging hydrogen 4-nitro-phthalate ligands. In the crystal, O-H⋯O and C-H⋯O hydrogen bonds link the ionic components into a three-dimensional supra-molecular framework, which is further reinforced by aromatic π-π stacking inter-actions between neighbouring phenanthroline and hydrogen 4-nitro-phthalate rings, with centroid-to-centroid separations ranging from 3.501 (5) to 3.687 (4) Å. Hirshfeld surface analysis shows that O⋯H/H⋯O contacts make the largest contribution (38.1%) to the crystal packing, confirming the dominant role of hydrogen bonding in consolidating the crystal structure.