A Cd(II) Luminescent Coordination Grid as a Multiresponsive Fluorescence Sensor for Cr(VI) Oxyanions and Cr(III), Fe(III), and Al(III) in Aqueous Medium

Hydro(solvo)thermal reactions of Cd(NO(3))(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-H(2)bdc) afforded a luminescent coordination polymer, {[Cd(Br-1,3-bdc)(NI-mbpy-34)(H(2)O)]∙2H(2)O}(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 (4(4)·6(2)), where the Cd(II) center adopts a {CdO(5)N(2)} 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 CH(2)Cl(2), H(2)O, CH(3)OH, and toluene. Photoluminescence studies indicated that 1 displayed intense blue fluorescence emissions in both solid-state and H(2)O 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 CrO(4)(2)(−) and 14.91 μM for Cr(2)O(7)(2)(−), through energy competition absorption mechanism. In addition, 1 could also sensitively detect Cr(3+), Fe(3+), and Al(3+) ions in aqueous medium via fluorescence-enhancement responses, with LOD = 2.81 μM for Cr(3+), 3.82 μM for Fe(3+), and 3.37 μM for Al(3+), mainly through an absorbance-caused enhancement (ACE) mechanism.