A fluorescent cobalt(Ⅱ) complex, 1 [Co(H2bibim)2(5-nipa)], for the recognition of cations and small molecules constructed with 5-nitroisophthalic acid (5-H2nipa) and 2,2-biben-zimidazole(H2bibim) has been synthesized by hydrothermal methods and structurally characterized by elemental analysis, IR spectroscopy, PL and single-crystal X-ray diffraction. The cobalt units are six-coordinated by two H2bibim ligands and one 5-nitroisophthalic acid group, which are further connected into a three-dimensional (3D) network by intermolecular hydrogen bonds. Complex 1 exhibits fluorescence and thus has detection capabilities for different cations and small solvent molecules in the solution state at room temperature. A fluorescent cobalt (II) complex, 1 [Co (H2bibim) 2 (5-nipa)] for the recognition of cations and small molecules constructed with 5- nitroisophthalic acid (5-H2nipa) and 2,2-bibenzimidazole H2bibim) has been synthesized by hydrothermal methods and structurally characterized by elemental analysis, IR spectroscopy, PL and single-crystal X-ray diffraction. The cobalt units are six-coordinated by two H2bibim ligands and one 5-nitroisophthalic acid group, which are further Complex 1 rendered fluorescence and thus has detection capabilities for different cations and small solvent molecules in the solution state at room temperature.