Thermodynamic relationships in complex formation. IX. DELTAH-DELTAS and free energy relationships in mixed ligand complex formation reactions of Cd(II) in aqueous solution

摘要

Standard thermodynamic parameters DELTAG, DELTAH and DELTAS for several series of coordiation reactions between mixed ligand complexes of Cd(II) and sigle entering groups in aqueous solution at T=298.15 K and constant ionic strength mu=1 for KNO_3 were inspected for the occurrence of enthalpy-entropy and free energy relationships. Both the series of reactions between constant substratum and variable ligands (Sub+L(i)=Sub-L_(i); i=variable) and the series of reactions between variable Cd(II) complex substrata and constant entering ligand (Sub_(i)+L=Sub_(i)-L; i=variable) disclose linear compensative DELTAH-DELTAS interplay (DELTAH=DELTAH_res+tauDELTAS). The parameters (DELTAH_res and tau) of the linear relationships do not discriminate within the coordination levels of the reacting substrata. The series Sub_i)+S_2O_3~(2-)=Sub_(i)-S_2O_3~(2-) is distinguished from the other series for more a favourable DELTAH_res. The series of reactions Sub_(i)+L=Sub_(i)-L (i=variable) shows a non-linear dependence of the substratum-to-ligand affinities on the overall thermodynamic stability of the reacting substrata. The exponential relationship Y=A+B exp (CX) is proposed for describing the dependencies. The general interpretation of the parameters A, B and C are given.