The reduction of the title compound has been studied polarographically in different aqueous media. Remarkable specific anion effects have been observed. In the presence of OH- ions there is a strong displacement of E1/2 towards negative values. This has been interpreted as due to a deprotonation of the Co(sep)3+ ion, which can be treated as an association with OH-. Using the DeFord-Hume equation, the association constants have been determined at a constant ionic strength (I) of 0.5 mol dm-3 (NaCl). Values of 50 mol dm-3 and 2 × 103 mol3 dm-9 have been obtained for β1 and β3, whereas β2 appears to be too small to be measured. These results are supported by visible spectrophotometric and circular dichroism data. Analogous polarographic measurements were performed at I = 0.4, 1.0 and 2.0 mol dm-3. The differences between the results in the various media, as well as the changes in E1/2 in neutral solutions with different supporting electrolytes, are correlated with the effects of the different salts on the solubility in water of benzoic acid and of naphthalene (Setchenov coefficients). Hence, the hydrophobic character of the anions seems to be more relevant than the electrostatic effects.
POLAROGRAPHIC AND SPECTROPHOTOMETRIC INVESTIGATION OF THE REDUCTION AND DEPROTONATION OF (1,3,6,8,10,13,16,19-OCTA-AZABICYCLO-[6,6,6]-ICOSANE)COBALT(III) ION, CO(SEP)3+, IN THE PRESENCE OF DIFFERENT ANIONS
DUATTI, Adriano;
1989
Abstract
The reduction of the title compound has been studied polarographically in different aqueous media. Remarkable specific anion effects have been observed. In the presence of OH- ions there is a strong displacement of E1/2 towards negative values. This has been interpreted as due to a deprotonation of the Co(sep)3+ ion, which can be treated as an association with OH-. Using the DeFord-Hume equation, the association constants have been determined at a constant ionic strength (I) of 0.5 mol dm-3 (NaCl). Values of 50 mol dm-3 and 2 × 103 mol3 dm-9 have been obtained for β1 and β3, whereas β2 appears to be too small to be measured. These results are supported by visible spectrophotometric and circular dichroism data. Analogous polarographic measurements were performed at I = 0.4, 1.0 and 2.0 mol dm-3. The differences between the results in the various media, as well as the changes in E1/2 in neutral solutions with different supporting electrolytes, are correlated with the effects of the different salts on the solubility in water of benzoic acid and of naphthalene (Setchenov coefficients). Hence, the hydrophobic character of the anions seems to be more relevant than the electrostatic effects.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
