| Abstrakt: |
The syntheses of N,N-bis-[(2-pyridylmethyl)]-1,3-diamidopropane (papH2) and N,N-bis-[(2-pyridylmethyl)]-1,3-diamido-2-hexadecylpropane (C16papH2) are reported together with the results of potentiometric titrations of papH2 with Co(II), Ni(II), Cu(II) and Zn(II), spectroscopic and electrochemical data of [Ni(pap)] and [Cu(pap)], structural studies involving the X-ray analyses of the metal-free papH2 ligand and the corresponding Ni(II) and Cu(II) complexes [Ni(pap)] × 2 H2O and [Cu(pap)] × 3 H2O, and force-field calculations (MM) of [Co(pap)], [Ni(pap)], [Cu(pap)] and [Zn(pap)] and the corresponding complexes of the ligand with ortho-methyl-substituted pyridyl groups (Me2papH2); the results of metal ion transport [Co(II), Ni(II), Cu(II) and Fe(II)] from aqueous solutions through C16papH2 containing dichloromethane phases are also given. The extractability with C16papH2 increases along the series Fe(II) < Co(II) < Ni(II) < Cu(II), and this is confirmed by the potentiometric data (papH2, aqueous solutions; logβML[Co(II)] = 1.75; logβMLH2[Ni(II)] = 11.49; logβML[Cu(II)] = 3.41; logβMLH2[Cu(II)] = 4.491; logβML[Zn(II)] = 1.87). The structural data (X-ray and MM) indicate that, due to the ortho protons of the pyridyl groups and in dependence of the electronic configuration of the metal center, there is a considerable tetrahedral twist of the central MN4 chromophores {square planar: θ = 0°; tetrahedral: θ = 90°; [Co(pap)]: θ = 15° (MM); [Ni(pap)]: θ = 16° (X-ray), 16° (MM); [Cu(pap)]: θ = 18° (X-ray), 18° (MM); [Zn(pap)]: θ = 23° (MM)}, and this may be enhanced by ortho-methyl substitution of the pyridyl donors {[Co(Me2pap)]: θ = 20° (MM); [Ni(Me2pap)]: θ = 20° (MM); [Cu(Me2pap)]: θ = 24° (MM); [Zn(Me2pap)]: θ = 31° (MM)}, and thus possibly a decrease in the complex stability of Cu(II) and Ni(II) in favor of Zn(II). |
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