Stability Constants and Thermodynamic Parameters of Complexes of Lanthanide Ions and (±)-Norvaline

Abstract

The protonation constants of (±)-norvaline and the stability constants of complexes between lanthanide ions and (±)-norvaline at various ionic strengths (I c/mol·dm-3 = 0.05, 0.10, and 0.15) at 300 K and at different temperatures (T/K = 300, 310, and 320) at I c = 0.05 mol·dm-3 were determined potentiometrically. The potassium nitrate solution was used to maintain the ionic strength. The stability constants show an inverse relationship with ionic strengths. The thermodynamic parameters based on these formation constants were calculated. The values of enthalpy change and entropy change are positive for all systems. The stability order obtained was La(III) < Pr(III) < Nd(III) < Tb(III). The formula of the complex is given and acid−ligand curves are interpreted. The thermodynamic stability constants (log ) obtained for the complexes of (±)-norvaline with La(III), Pr(III), Nd(III), and Tb(III) were 5.57, 5.94, 5.96, and 6.55, respectively.

Potentiometry and geometrical structure of some azodye compounds and their metal complexes

“…This is caused by the negative indicative effect of the NO 2 group, which decreases its ability for chelation, and therefore the stability of the complexes. (iv) For the ligands with the same metal ion at constant temperature, the stability of the chelates increases in the order HL I N HL II N HL III [36]. (v) The stability constants of Mn 2+ , Co 2+ , Ni 2+ and Cu 2+ complexes were increased with increasing atomic number in the order Cu 2+ N Ni 2+ N Co 2+ N Mn 2+ at constant temperature as shown in Figs.…”

“…(iii) The metal titration curves were displaced to the right-hand side of the ligand titration curves along the volume axis, indicating proton release upon complex formation of the metal ion with the ligand. The large decrease in pH for the metal titration curves relative to ligand titration curves points to the formation of strong metal complexes [36]. (iv) In most cases, the color of the solution after complex formation was observed to be different from the color of the ligand at the same pH.…”

Stereochemistry of New Nitrogen Containing Heterocyclic Aldehyde. VII. Potentiometric, Conductometric and Thermodynamic Studies of Novel Quinoline Azodyes and Their Metal Complexes with Some Transition Metals.

“…The large decrease in pH for the metal titration curves relative to ligand titration curves point to the formation of strong metal complexes. 28) iv) In most cases, the colour of the solution after complex formation was observed to be different from the colour of the ligand at the same pH. v) For the same ligand at constant temperature, the stability of the chelates increases in the order Cu .…”

Geometrical structure, potentiometric and thermodynamic studies of rhodanine azodye and its metal complexes

“…(iii) The metal titration curves were displaced to the right-hand side of the ligand titration curves along the volume axis, indicating proton release upon complex formation of the metal ion with the ligand. The large decrease in pH for the metal titration curves relative to ligand titration curves points to the formation of strong metal complexes [39,40]. (iv) At constant temperature, the stability of the chelates increases in the order Cu 2+ N Ni 2+ N Co 2+ N Mn 2+ [41][42][43].…”