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), in aqueous medi a. The cadmium triflate salt concentration dependence is explainable by the formation of a bis-triflate coordination compound having an overall format ion constant of (4 +/- 0.5) x 10(-3). The chemical shift for Cd(tf), is fou nd to be - 180 ppm from that of the aqueous Cd(II) ion. The data analysis i s 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 th e experimental chemical shift from the predicted behavior for a simple bis complex equilibrium upon addition of a large excess of triflic acid to a di lute cadmium solution, indicates either the formation of higher complexes o r increases in the formation constant for the bis species caused by decreas es in the solvent dielectric constant. (C) 2000 Elsevier Science S.A. All r ights reserved.