Fluorescence sensing of nitro-aromatics by Zn(II) and Cd(II) based coordination polymers having the 5-[bis(4-carboxybenzyl)-amino]isophthalic acid ligand

Three new coordination polymers (CPs) viz. [Zn-2(L)](n) (1), {[Cd-3(L)(2)(H2O)][Na-2(mu(2)-H2O)(H2O)(7)]}(n) (2) and [Zn-2(L)(phen)(2)(H2O)center dot H2O](n) (3) were synthesized by the reaction between 5-[bis(3-carboxybenzyl)-amino]isophthalic acid (H4L) Zn(NO3)(2) (1)/Cd(NO3)(2) (2) or Zn(NO3)(2) and H4L in the presence of 1,10-phenanthroline (phen) (3) and characterized. X-ray single-crystal analyses reveal that 1 possesses a 3D architecture with a {4.6(2)}{4.8(2)}{4(2).6(5).8(8)} topology, whereas 2 shows a unique (4,8)-connected 3D framework with a {4(11).6(15).8(2)}{4(5).6}{4(6)} topology. In the case of 3, the L and phen ligands linked the Zn(II) atoms into a deeply corrugated 2D sheet. The results showed that the structural diversity of the polymers resulted from the different geometries of the metal ions and the effect of the assistant ligands. The photoluminescence sensing of nitro-aromatics by 1-3 indicates that these CPs could be prospective candidates for developing luminescence sensors for selective sensing of these species. Theoretical and experimental investigations indicate that the observed quenching in the photoluminescence intensities of 1-3 by nitro-aromatics may be assigned to the occurrence of both electron and energy transfer processes, in addition to electrostatic interaction between the CPs and nitro-aromatics.