| Summary: | A pair of cobalt(II)-based hydrogen-bonded organic frameworks (HOFs), [Co(pca)<sub>2</sub>(bmimb)]<i><sub>n</sub></i> (<b>1</b>) and [Co<sub>2</sub>(pca)<sub>4</sub>(bimb)<sub>2</sub>] (<b>2</b>), where Hpca = <i>p</i>-chlorobenzoic acid, bmimb = 1,3-bis((2-methylimidazol-1-yl)methyl)benzene, and bimb = 1,4-bis(imidazol-1-ylmethyl)benzene were hydrothermally synthesized and characterized through infrared spectroscopy (IR), elemental and thermal analysis (EA), power X-ray diffraction (PXRD), and single-crystal X-ray diffraction (SCXRD) analyses. X-ray diffraction structural analysis revealed that <b>1</b> has a one-dimensional (1D) infinite chain network through the deprotonated pca<sup>−</sup> monodentate chelation and with a μ<sub>2</sub>-bmimb bridge Co(II) atom, and <b>2</b> is a binuclear Co(II) complex construction with a pair of symmetry-related pca<sup>−</sup> and bimb ligands. For both <b>1</b> and <b>2</b>, each cobalt atom has four coordinated twisted tetrahedral configurations with a N<sub>2</sub>O<sub>2</sub> donor set. Then, <b>1</b> and <b>2</b> are further extended into three-dimensional (3D) or two-dimensional (2D) hydrogen-bonded organic frameworks through C–H···Cl interactions. Topologically, HOFs <b>1</b> and <b>2</b> can be simplified as a 4-connected <b><i>qtz</i></b> topology with a Schläfli symbol {6<sup>4</sup>·8<sup>2</sup>} and a 4-connected <b><i>sql</i></b> topology with a Schläfli symbol {4<sup>4</sup>·6<sup>2</sup>}, respectively. The fluorescent sensing application of <b>1</b> was investigated; <b>1</b> exhibits high sensitivity recognition for Fe<sup>3+</sup> (<i>K</i><sub>sv</sub>: 10970 M<sup>−1</sup> and detection limit: 19 μM) and Cr<sub>2</sub>O<sub>7</sub><sup>2−</sup> (<i>K</i><sub>sv</sub>: 12960 M<sup>−1</sup> and detection limit: 20 μM). This work provides a feasible detection platform of HOFs for highly sensitive discrimination of Fe<sup>3+</sup> and Cr<sub>2</sub>O<sub>7</sub><sup>2−</sup> in aqueous media.
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