NMR study of cadmium(II)–triflate coordination

The coordination of cadmium(II) in triflic acid media is evaluated from the NMR chemical shift variation with concentration of Cd(tf)2 in aqueous media. The cadmium triflate salt concentration dependence is explainable by the formation of a bis-triflate coordination compound having an overall formation constant of (4±0.5)×10−3. The chemical shift for Cd(tf)2 is found to be −180 ppm from that of the aqueous Cd(II) ion. The data analysis is consistent with either no mono complex formation or a chemical shift for the mono complex that is equal to that of the aqueous ion. Divergence of the experimental chemical shift from the predicted behavior for a simple bis complex equilibrium upon addition of a large excess of triflic acid to a dilute cadmium solution, indicates either the formation of higher complexes or increases in the formation constant for the bis species caused by decreases in the solvent dielectric constant.