Bismuth(III) complexes of D-gluconic acid. Studies in aqueous solution andin the solid phase

The system formed between bismuth(III) ion and D-gluconic acid was potendom etrically studied in aqueous solution. Measurements were carried out at 20. 0 and 25.0+/-0.1 degrees C and the ionic strength was maintained at 0.100 M with NaNO3. The potentiometric curves showed the release of four protons i n addition to the carboxylic one, leading to the formation of complexes wit h different degrees of deprotonation. Since the first chelate was completel y formed at low pH, competition equilibria involving ethylenediaminetetraac etic acid or nitrilotriacetic acid ligands were used to calculate the corre sponding equilibrium constant. Coordination bonding sites for metal-ligand interactions were inferred from C-13 NMR spectroscopy. According to the obt ained results, the complex formed at acid pH would present a carboxylate co ordination and those formed at high pH would involved a bonding with the ox ygens of carbons 2, 3, 4 and 5. On the other hand, the complex Bi(C6H9O7). H2O was isolated and characterized by elemental and thermogravimetric analy ses and by Fourier transform infra-red (FT-IR) spectroscopy. While the ther mogravimetric analyses confirmed the water content in the solid complex, th e IR spectra showed a monodentate carboxylate coordination. (C) 1999 Elsevi er Science Ltd. All rights reserved.