A new Cd(ii)-based coordination polymer as a luminescent sensor and adsorbent for dichromate ions

Abstract

Coordination polymers (CPs) with a d¹⁰-configuration containing metal cations offer interesting photoluminescent properties and hence can be employed as sensors to detect various classes of analytes. Moreover, due to their tuneable pore size they can be employed as adsorbents for various species. Herein, a new d¹⁰-configuration Cd(II)-based CP with composition {[Cd(bip)₄(H₂O)₂]_n·2NO₃} (1) (bip = 3,5-bis(1-imidazol)pyridine) has been synthesized and characterized. Single-crystal X-ray analysis reveals that the Cd(II) center adopts octahedral geometry that is satisfied by four N atoms from the four bip linkers and two aqua ligands, and the resultant CP displays sql topology with the point symbol of (4⁴·6²). The CP offers prospective application as a photoluminescent sensor for dichromate anions with a limit of detection of 1.28 ppm and a Stern–Volmer constant (K_SV) of 1.51 × 10⁵. Furthermore, CP 1 was employed as an efficient adsorbent for dichromate ions, reaching an equilibrium adsorption capacity of 389.82 mg g⁻¹ within 80 min. The effects of temperature, pH and concentration of dichromate were further investigated, which revealed that CP 1 displays the best adsorption at 30 °C and pH 4 with a dichromate concentration of 200 mg L⁻¹. The possible adsorption mechanism has been proposed with the aid of Hirshfeld surface analysis.