Synthesis, Structures and Recognition Properties of Two Cadmium(II) Phosphonates for Highly Selective Sensing of Cr 2 O 7 2− and CrO 4 2− Anions

Abstract Two cadmium (II) phosphonates, [Cd(MPBP)(2, 2′−bipy)(H 2 O)]⋅H 2 O ( 1 ) and [Cd(H 2 BPDP)(2,2′−bipy) 2 (H 2 O)]⋅H 2 O ( 2 ) [H 2 MPBP=4,4−Bis(monoethylphosphonomethyl)biphenyl, H 4 BPDP=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 H 2 MPBP as the phosphonate ligand and 2,2′−bipyridine as the second organic ligand. The compound 1 exhibited a 3D supramolecular structure, in which {CdN 2 O 4 } polyhedra and {CPO 3 } 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 Cr 2 O 7 2− and CrO 4 2− 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.