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.