Construction of Two Stable Co(II)-Based Hydrogen-Bonded Organic Frameworks as a Luminescent Probe for Recognition of Fe3+ and Cr2O72- in H2O

A pair of cobalt(II)-based hydrogen-bonded organic frameworks (HOFs), [Co(pca)(2)(bmimb)](n) (1) and [Co-2(pca)(4)(bimb)(2)] (2), where Hpca = p-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 1 has a one-dimensional (1D) infinite chain network through the deprotonated pca(-) monodentate chelation and with a mu(2)-bmimb bridge Co(II) atom, and 2 is a binuclear Co(II) complex construction with a pair of symmetry-related pca(-) and bimb ligands. For both 1 and 2, each cobalt atom has four coordinated twisted tetrahedral configurations with a N2O2 donor set. Then, 1 and 2 are further extended into three-dimensional (3D) or two-dimensional (2D) hydrogen-bonded organic frameworks through C-H & BULL;& BULL;& BULL;Cl interactions. Topologically, HOFs 1 and 2 can be simplified as a 4-connected qtz topology with a Schlafli symbol {6(4)& BULL;8(2)} and a 4-connected sql topology with a Schlafli symbol {4(4)& BULL;6(2)}, respectively. The fluorescent sensing application of 1 was investigated; 1 exhibits high sensitivity recognition for Fe3+ (K-sv: 10970 M-1 and detection limit: 19 mu M) and Cr2O72- (K-sv: 12960 M-1 and detection limit: 20 mu M). This work provides a feasible detection platform of HOFs for highly sensitive discrimination of Fe3+ and Cr2O72- in aqueous media.