Effect of Halide Complexation of Cadmium(II) on Cadmium-113 Chemical Shifts

A unique combination of solution and solid-state ¹¹³Cd NMR experiments has been employed to elucidate the ¹¹³Cd chemical shifts of the individual halide complexes of CdX⁺, CdX₂, CdX₃^-, and CdX₄^2-, where X is CI^-, Br^-, and I^-. The solution-state experiments made use of standard pulsed Fourier transform NMR techniques to examine the ¹¹³Cd chemical shift of aqueous 0.1 M Cd(C10₄)₂ as a function of halide concentration. The solid-state experiments made use of cross-polarization/ magic angle spinning techniques to examine the ^1l3Cd chemical shifts of a series of solid Cd(II)-halide complexes. By consideration of the appropriate multiple equilibria in solution together with,^1l3Cd chemical shift “benchmarks” from solid-state Cd(II)-halide complexes, the ll3Cd chemical shifts for the individual Cd(II)-halide complexes were derived. The following shielding orders are observed: Cd²⁺ > CdCl⁺ > CdCl₂ > CdCl₆^4-≥ CdCl₅^3- CdCl³> CdCl₄^2- for the Cd(II)-chloride complexes, Cd²⁺ > CdBr⁺≃ CdBr₂ > CdBr₃≃ CdBr₄^2- for the Cd(II)-bromide complexes, and Cd²⁺> Cdl⁺ > Cdl₄^2- > Cdl₃-for the Cd(ll)-iodide complexes.