Transition metal coordination compounds of bisamidobispyridyl ligands

The syntheses of N,N'-bis-[(2-pyridylmethyl)]-1,3-diamido propane (papH(2)) and N,N'-bis-[(2-pyridylmethyl)]-1,3-diamido-2-hexadecylpropane (C(16)papH(2)] are reported together with the results of potentiometric titrations of papH(2) 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 papH(2) ligand and the corresponding Ni(II) and Cu(II) complexes [Ni(pap)] X 2 H2O and [Cu(pap)] X 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 (Me(2)papH(2)); the results of metal ion transport [Co(II), Ni(II), Cu(II) and Fe(II)] from aqueous solutions through C(16)papH(2) containing dichloromethane phases are also given. The extractability with C(16)papH(2) increases along the series Fe(II) < Co(II) < Ni(II) < Cu(II), and this is confirmed by the potentiometric data (papH(2)) aqueous solutions; log beta(ML)[Co(II)] = 1.75; log beta(MLH-2)[Ni(II)] =-11.49; log beta(ML)[Cu(II)]=3.41; log beta(MLH-2)(-)[Cu(II)] = -4.491; log beta(ML)[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: theta = 0 degrees; tetrahedral: theta = 90 degrees; [Co(pap)]: theta = 15 degrees (MM); [Ni(pap)]: theta=16 degrees (X-ray), 16 degrees (MM); [Cu(pap)]: theta=18 degrees(X-ray),18 degrees (MM); [Zn(Pap)]: theta = 23 degrees (MM)), and this may be enhanced by ortho-methyl substitution of the pyridyl donors ([Co(Me(2)pap)]: theta = 20 degrees (MM); [Ni(Me(2)pap)]: theta = 20 degrees (MM); [Cu(Me(2)pap)]: theta = 24 degrees (MM); [Zn(Me(2)pap)]: theta = 31 degrees (MM)}, and thus possibly a decrease in the complex stability of Cu(II) and Ni(II) in favor of Zn(II).