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

A variety of complexes of cadmium with mono- and di-carboxylic acids in aqueous solution were investigated using Cd-113 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 range delta -22 to -24 and -39 to -40 for [CdL](+) and [CdL(2)] (L = carboxylate) species respectively: carboxylates with higher basicity tend to increase the shielding of the cadmium in the complexes. Tn case of dicarboxylic acids HO2C(CH2)(n)CO2H (n = 0-3) the Cd-113 nucleus showed greater shielding with increasing n. The upheld 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.