Two new luminescent Cd(ii)-based coordination polymers by regulating the asymmetrical tetracarboxylate and auxiliary ligands displaying high sensitivity for Fe3+ and CrO42−

Abstract

Two new coordination polymers (CPs), namely [Cd₂(L)(2,2′-bipy)] (1) and [Cd₂(L)(H₂O)₄] (2) (H₄L = [1,1′-biphenyl]-2,3,3′,5′-tetracarboxylic acid and 2,2′-bipy = 2,2′-bipyridine), have been successfully synthesized under solvothermal conditions. 1 exhibits a 2D layer that was further extended into a 3D supramolecular framework through the packing interaction. 2 has a 3D 3,3,4-c network with a point symbol of (6²·8²)(6³)₂. The sensing results illustrated that both of them could be prospective candidates for developing luminescent sensors for the probing of Fe³⁺ and CrO₄²⁻. The probe effects remained highly selective to the Fe³⁺ and CrO₄²⁻ ions even if there are other interfering ions. The limits of detection (LODs) for Fe³⁺/CrO₄²⁻ were calculated to be ca. 2.47 × 10⁻⁸ M⁻¹/1.12 × 10⁻⁸ M⁻¹ and 1.35 × 10⁻⁹ M⁻¹/2.23 × 10⁻⁸ M⁻¹ for 1 and 2, respectively. The fluorescence resonance energy transfer process may be the major pathway behind the quenching mechanism for Fe³⁺ and CrO₄^2- ions. The recycling operation indicated that compounds 1 and 2 are promising reusable probes for their effective capability of detecting Fe³⁺ and CrO₄²⁻ ions.