Abstract
The synthesis, acid-base equilibria and metal-ion chelating tendencies of 2,5-pyrrole-diylbis [ N-( o-hydroxyphenylaldimine)] (SBH 2) are reported. From potentiometric equilibrium measurements of hydrogen-ion concentration at 10, 20, and 30°C and ionic strength 0.10 M KNO 3 in 75% ( v v ) dioxan-water medium, the stability constants and the thermodynamic parameters (free energy, enthalpy and entropy) of SBH 2 complexes with transition, non-transition and lanthanide ions have been evaluated. The higher values of free energy Δ G, enthalpy Δ H and entropy Δ S of copper(II) complexes compared with those of other metal complexes were attributed to the unique electron configuration d 9 of Cu(II) ions, which is subject to the Jahn-Teller effect. The relation between the thermodynamic parameters of lanthanide complexes and the reciprocal of the cationic radius (1 / r) of lanthanide cations was not linear, as would be expected from the ionic model. The use of SBH 2 as an analytical reagent for spectrophotometric determination of copper, nickel, cobalt, and uranium is discussed.
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