Synthesis, Structures and Recognition Properties of Two Cadmium(II) Phosphonates for Highly Selective Sensing of Cr2O72− and CrO42− Anions

Abstract

AbstractTwo cadmium (II) phosphonates, [Cd(MPBP)(2, 2′−bipy)(H2O)]⋅H2O (1) and [Cd(H2BPDP)(2,2′−bipy)2(H2O)]⋅H2O (2) [H2MPBP=4,4−Bis(monoethylphosphonomethyl)biphenyl, H4BPDP=biphenyl−4,4′−diylbis(methylene)diphosphonic acid, 2,2′−bipy=2,2′−bipyridine], had been successfully synthesized under hydrothermal conditions with different reaction temperatures by using H2MPBP as the phosphonate ligand and 2,2′−bipyridine as the second organic ligand. The compound 1 exhibited a 3D supramolecular structure, in which {CdN2O4} polyhedra and {CPO3} tetrahedra were interconnected by MPBP anions to form a 1D double chain via corner–sharing. Neighboring chains were linked into a 2D supramolecular sheet in the ac–plane by hydrogen bonding interactions, which were further assembled through π−π stacking interactions to form a 3D supramolecular structure. Compound 2 was assembled through π−π stacking and hydrogen bonding interactions to form a 1D supramolecular structure. Furthermore, both compounds exhibited remarkable luminescent properties, and could be applied as the high selective and sensitive luminescent sensors in the sensing of Cr2O72− and CrO42− anions through the luminescence quenching effect with a low–detection limit of 3.5 × 10−7 M and 4.6 × 10−7 M (for 1) and 6.1 × 10−7 M and 4.3 × 10−7 M (for 2), respectively. Additionally, the probable mechanisms for the quenching behaviour for the two compounds had also been investigated in detail.