Fluorescence-Responsive Detection of Ag(I), Al(III), and Cr(III) Ions Using Cd(II) Based Pillared-Layer Frameworks

Two Cd(II) based coordination polymers, {Cd(3)(btc)(2)(BTD-bpy)(2)]∙1.5MeOH∙4H(2)O}(n) (1) and [Cd(2)(1,4-ndc)(2)(BTD-bpy)(2)](n) (2), where BTD-bpy = bis(pyridin-4-yl)benzothiadiazole, btc = benzene-1,3,5-tricarboxylate, and 1,4-ndc = naphthalene-1,4-dicarboxylate, were hydro(solvo)thermally synthesized. Compound 1 has a three-dimensional non-interpenetrating pillared-bilayer open framework with sufficient free voids of 25.1%, which is simplified to show a topological (4,6,8)-connected net with the point symbol of (3(2)4(2)56)(3(4)4(4)5(4)6(2)8)(3(4)4(2)6(19)7(2)8). Compound 2 has a three-dimensional two-fold interpenetrating bipillared-layer condense framework regarded as a 6-connected primitive cubic (pcu) net topology. Compounds 1 and 2 both exhibited good water stability and high thermal stability approaching 350 °C. Upon excitation, compounds 1 and 2 both emitted blue light fluorescence at 471 and 479 nm, respectively, in solid state and at 457 and 446 nm, respectively, in the suspension phase of H(2)O. Moreover, compounds 1 and 2 in the suspension phase of H(2)O both exhibited a fluorescence quenching effect in sensing Ag(+), attributed to framework collapse, and a fluorescence enhancement response in sensing Al(3+) and Cr(3+), ascribed to weak ion–framework interactions, with high selectivity and sensitivity and low detection limit.