Hydro(solvo)thermal reactions of Cd(NO3)2, N-(pyridin-3-ylmethyl)-4-(pyridin-4-yl)-1,8-naphthalimide (NI-mbpy-34), and 5-bromobenzene-1,3-dicarboxylic acid (Br-1,3-H2bdc) afforded a luminescent coordination polymer, {[Cd(Br-1,3-bdc)(NI-mbpy-34)(H2O)]∙2H2O}n (1). Single-crystal X-ray diffraction analysis showed that 1 features a two-dimensional (2-D) gridlike sql layer with the point symbol of (44·62), where the Cd(II) center adopts a {CdO5N2} pentagonal bipyramidal geometry. Thermogravimetric (TG) analysis confirmed the thermal stability of 1 up to about 340 °C, whereas XRPD patterns proved the maintenance of crystallinity and framework integrity of 1 in CH2Cl2, H2O, CH3OH, and toluene. Photoluminescence studies indicated that 1 displayed intense blue fluorescence emissions in both solid-state and H2O suspension-phase. Owing to the good fluorescent properties, 1 could serve as an excellent turn-off fluorescence sensor for selective and sensitive Cr(VI) detection in water, with LOD = 15.15 μM for CrO42- and 14.91 μM for Cr2O72-, through energy competition absorption mechanism. In addition, 1 could also sensitively detect Cr3+, Fe3+, and Al3+ ions in aqueous medium via fluorescence-enhancement responses, with LOD = 2.81 μM for Cr3+, 3.82 μM for Fe3+, and 3.37 μM for Al3+, mainly through an absorbance-caused enhancement (ACE) mechanism.
Keywords: Cr(VI) oxyanion; coordination polymer; luminescence sensor; trivalent metal ion.