Eu(fod)₃ binding on the ¹H-NMR spectra of bis(2′-ethylbenzoate)ethylene glycol podands

The complexing and selective binding constants of Eu(fod)₃ with bis(2′-ethylbenzoate)ethylene glycol podands having one to four oxyethylene groups was observed on their ¹H-NMR spectra at 250 MHz and 295 K in CDCl₃. The Eu(fod)₃ interaction displayed the selective binding role of oxygen on H₂C-O-CH₂ backbones with referring the ¹H chemical shifts. The estimated equilibrium constants, K_a, of 1:1 ratio of interactions were in accordance with the Eu(fod)₃ ionic radii to bind the oxygen sites depending on the size and conformation of the esters. Esters having one or two ethyleneoxy groups gave mainly 2:2 complexes using ester sites. The minimum lanthanide-podand ester distance displayed the maximum stability so that ester with four oxyethylene groups was found to bind the Eu(fod)₃ moderately, whereas ester with three oxyethylene groups showed a large induced chemical shift due to the stability of Eu³⁺ complexes with larger ethyleneoxy groups.