| Popis: |
Transfer from water to nitrobenzene of Iron(II) and (III), Ni(II) and Zn(II) complexed in the aqueous phase by one, two and three molecules of o-phenanthroline and o,o'-bipyridine was investigated using cyclic voltammetry. The kinetically inert complexes of Fe(II), Fe(III) and Ni(II) are keeping their ligand-metal bonds intact and are transferred reversibly from water into nitrobenzene. The uncomplexed metal ions are not transferred within the voltage range limited by transfer of the ions of the aqueous and nonaqueous supporting electrolyte. Ease of phase-transfer is greatly enhanced by complexation with the organic ligand and successive addition of the first, second and third bidentate nitrogen base changes the Gibb's transfer enthalpy of the Ni(II) by approximately equal amounts (ΔΔG° ≈ − 37 kJ/Mol;). The molecular structure of the complex ligand bears only a minor but clearly discernible influence on the Gibb's transfer enthalpies as demonstrated for Ni(II)-phenanthroline and bipyridine complexes. Comparative investigation of phase transfer of Fe(II)-and Fe(III)-trisphenanthroline complexes reveals that due to higher charge of the Fe(III)-complexes they are more strongly solvated in aqueous solution and hence less easily extracted into nitrobenzene than Fe(II)- complexes. Voltammograms for transfer of complexed zinc ions which form kinetically (fast) labile complexes in water as well as in nitrobenzene are to a great deal determined by fast homogeneous kinetics. - In particular mono- and bicomplexed zinc ions (ZnL2+ and ZnL2+2) undergo rapid disproportionation with preferential formation of triscomplexed zinc (ZnL2+3) in the nonaqueous phase. Diffusion coefficients of differently complexed species in water are determined and show a shift to lower values with increasing degree of complexation. |
Plný text