Crystal structure of poly[[{μ(2)-1,4-bis[(1H-imid­azol-1-yl)methyl]benzene}[μ(6)-5-(4-carboxylatophenoxy)isophthalato]-μ(3)-hydroxido-dicobalt(II)] 0.25-hydrate]

The title coordination polymer, {[Co(2)(C(15)H(7)O(7))(OH)(C(14)H(14)N(4))]·0.25H(2)O}(n), was synthesized under hydro­thermal conditions. The asymmetric unit contains two Co(2+) ions, one L (3−) anion originating from 5-(4-carb­oxy­phen­oxy)isophthalic acid (H(3) L), one OH(−) ligand, one 1,4-bis­[(1H-imidazol-l-yl)meth­yl]benzene (bix) ligand and one disordered lattice water mol­ecule (occupancy 0.25). The two Co(2+) ions have different environments. One has an octa­hedral O(4)N(2) coordin­ation sphere, defined by four O atoms from three carboxyl­ate groups and one OH(−) ligand, and two N atoms from two symmetry-related bix ligands. The other has a trigonal-bipyramidal O(5) coordination sphere resulting from three carboxyl­ate groups and two OH(−) ligands. The dihedral angles between the two benzene rings in the L (3−) ligand and between the benzene ring and the two imidazole rings in the bix ligand are 67.05 (15), 75.27 (17) and 82.05 (17)°, respectively. Four neighbouring Co(2+) ions are linked by six carboxyl­ate groups and two μ (3)-OH ligands, forming a butterfly-shaped secondary building unit (SBU). These SBUs are connected by L (3−) anions into layers parallel to (1-10). Adjacent layers are cross-linked by the bix ligands, forming a three-dimensional framework that has a bimodal (3,8)-connected tfz-d topology. The disordered lattice water mol­ecule is located in the voids of the framework and has O⋯O and O⋯N contacts of 2.81 (2) and 2.95 (2) Å, suggesting medium-strength hydrogen bonds. The title compound may be a good candidate for artificial eye lenses.