Cd NMR Studies of Small Dynamically Stable Cd²⁺ Complexes

¹¹³Cd and ¹³C NMR spectra have been obtained on several dynamically stable cadmium complexes. In several cases a ¹³C-¹¹³Cd three-bond coupling has been observed and utilized in the assignment of the ¹³C NMR spectra. The pH dependence of the ¹¹³Cd resonance from the cadmium-ethylenediamine-N,N,N′,N′-tetraphosphonate complex shows that this complex has two acid dissociation constants, pK_a= 7.85 and 8.80, respectively. ¹¹³Cd nuclear Overhauser effect, NOE, =1 + η, and spin lattice relaxation time, T₁, were determined on all the complexes and used in the analysis of the contribution to the relaxation mechanism from the dipolar interaction with protons and chemical shift anisotropy. Together, the multinuclear NMR parameters contribute to a detailed understanding of the structure and dynamics of these metal complexes. Furthermore, the ¹¹³Cd NMR parameters from these model complexes provide important new data relevant to the interpretation of the ¹¹³Cd NMR parameters from biological systems.