Cadmium-113 nuclear magnetic resonance studies of cadmium(II)—carboxylate complexes in aqueous solution

Abstract

A variety of complexes of cadmium with mono- and di-carboxylic acids in aqueous solution were investigated using ¹¹³Cd NMR spectroscopy. A single averaged chemical shift was obtained even at reduced temperature, showing that the cadmium–monocarboxylate complexes are undergoing rapid exchange in solution. Using the known stability constants, the individual chemical shifts were calculated to be in the ranges δ–22 to –24 and –39 to –40 for [CdL]⁺ and [CdL₂](L = carboxylate) species respectively: carboxylates with higher basicity tend to increase the shielding of the cadmium in the complexes. In case of dicarboxylic acids HO₂C(CH₂)_nCO₂H (n= 0–3) the ¹¹³Cd nucleus showed greater shielding with increasing n. The upfield chemical shift observed for the dialkyl-substituted malonate complexes of Cd^II compared to the malonate complex is caused by the steric effect hindering ring formation.