The asymmetric compartmental macrocycles containing one N2O2 or N3O2 Schiff base and one O2O3 or O2O4 crown-ether like chamber, have been obtained by condensation reaction of the formyl precursors 3,3-(3-oxapentane-1,5-diyldioxy)bis(2-hydroxybenzaldehyde) or 3,3-(3,6-dioxaoctane-1,8-diyldioxy)bis(2-hydroxybenzaldehyde) with ethylenediamine (H2LA,H2LC) or 1,5-diamino-3-azamethylpentane(H2LB,H2LD), also in the presence of metal ions as templating agents. These ditopic ligands, with dissimilar coordination sites, have been designed and used for the selective complexation of d and/or s metal ions, respectively into the Schiff base and the crown ether chamber. The selectivity of these processes strongly depends on the size and on the donor atom sets of the sites. The possibility to obtain mononuclear M(L)nH2O (M = Ni2+, Cu2+, Co2+), Mn(L)(CH3COO)nH2O or Na(L) and hetero-dinuclear MNa(L)(CH3COO)( M = Ni2+, Cu2+, Co2+) and MnNa(L)(CH3COO)2nH2O complexes has been successfully tested. The ligands and complexes have been characterized by ir, nmr, mass spectrometry and magnetic susceptibility measurements. Two of the ligands used for the preparation of the solid samples, i.e. to H2LA and H2LB,were employed to study complexation reactions of Co(II) and Na(I) in solution. In order to obtain information on the ligand preorganization effect toward the complex stabilities, a simpler open chain parent compound of H2LB (H2LE) was also prepared and studied. FT-IR spectra show that H2LA is unable to complex Na+ in DMSO while the complexation reactions of Na+ by H2LB and of Co2+ by H2LA take place with slow kinetics. Therefore, thermodynamic data could be obtained only for the systems Co2+/H2LB and Co2+/H2LE The thermodynamic parameters obtained for the complexation reactions show that the pre-organization of the donor atoms in H2LB does not add a significant contribution to the stabilities of the complexes. Both H2LB and H2LE form in DMSO 1:1, 1:2 and 1:3 = M:L complexes with very similar stabilities and almost equal enthalpies of formation. Physico-chemical studies suggest besides that the slow reaction of Na+ with H2LB is probably due to the formation of a 1:1 complex where the metal cation, initially occupying the O3 cage of the ligand, slowly binds also the oxygens of the phenolic moieties. Spectral and calorimetric data on solutions containing H2LB and different Co2+: Na+ ratios evidence that in DMSO no stable heterodinuclear complexes form when the neutral ligand is considered.
New complexes of ditopic ligands with "d" and/or "s" metal ions
Tamburini S;Tomasin P;Vigato PA
2001
Abstract
The asymmetric compartmental macrocycles containing one N2O2 or N3O2 Schiff base and one O2O3 or O2O4 crown-ether like chamber, have been obtained by condensation reaction of the formyl precursors 3,3-(3-oxapentane-1,5-diyldioxy)bis(2-hydroxybenzaldehyde) or 3,3-(3,6-dioxaoctane-1,8-diyldioxy)bis(2-hydroxybenzaldehyde) with ethylenediamine (H2LA,H2LC) or 1,5-diamino-3-azamethylpentane(H2LB,H2LD), also in the presence of metal ions as templating agents. These ditopic ligands, with dissimilar coordination sites, have been designed and used for the selective complexation of d and/or s metal ions, respectively into the Schiff base and the crown ether chamber. The selectivity of these processes strongly depends on the size and on the donor atom sets of the sites. The possibility to obtain mononuclear M(L)nH2O (M = Ni2+, Cu2+, Co2+), Mn(L)(CH3COO)nH2O or Na(L) and hetero-dinuclear MNa(L)(CH3COO)( M = Ni2+, Cu2+, Co2+) and MnNa(L)(CH3COO)2nH2O complexes has been successfully tested. The ligands and complexes have been characterized by ir, nmr, mass spectrometry and magnetic susceptibility measurements. Two of the ligands used for the preparation of the solid samples, i.e. to H2LA and H2LB,were employed to study complexation reactions of Co(II) and Na(I) in solution. In order to obtain information on the ligand preorganization effect toward the complex stabilities, a simpler open chain parent compound of H2LB (H2LE) was also prepared and studied. FT-IR spectra show that H2LA is unable to complex Na+ in DMSO while the complexation reactions of Na+ by H2LB and of Co2+ by H2LA take place with slow kinetics. Therefore, thermodynamic data could be obtained only for the systems Co2+/H2LB and Co2+/H2LE The thermodynamic parameters obtained for the complexation reactions show that the pre-organization of the donor atoms in H2LB does not add a significant contribution to the stabilities of the complexes. Both H2LB and H2LE form in DMSO 1:1, 1:2 and 1:3 = M:L complexes with very similar stabilities and almost equal enthalpies of formation. Physico-chemical studies suggest besides that the slow reaction of Na+ with H2LB is probably due to the formation of a 1:1 complex where the metal cation, initially occupying the O3 cage of the ligand, slowly binds also the oxygens of the phenolic moieties. Spectral and calorimetric data on solutions containing H2LB and different Co2+: Na+ ratios evidence that in DMSO no stable heterodinuclear complexes form when the neutral ligand is considered.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
