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

The system formed between bismuth(III) ion and D-gluconic acid was potendometrically 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 in addition to the carboxylic one, leading to the formation of complexes with different degrees of deprotonation. Since the first chelate was completely formed at low pH, competition equilibria involving ethylenediaminetetraacetic acid or nitrilotriacetic acid ligands were used to calculate the corresponding equilibrium constant. Coordination bonding sites for metal-ligand interactions were inferred from C-13 NMR spectroscopy. According to the obtained results, the complex formed at acid pH would present a carboxylate coordination and those formed at high pH would involved a bonding with the oxygens of carbons 2, 3, 4 and 5. On the other hand, the complex Bi(C6H9O7). H2O was isolated and characterized by elemental and thermogravimetric analyses and by Fourier transform infra-red (FT-IR) spectroscopy. While the thermogravimetric analyses confirmed the water content in the solid complex, the IR spectra showed a monodentate carboxylate coordination. (C) 1999 Elsevier Science Ltd. All rights reserved