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Synthesis and coordination properties of new macrocyclic ligands: equilibrium studies and crystal structures

2004; Royal Society of Chemistry; Issue: 21 Linguagem: Inglês

10.1039/b408808e

1477-9234

Gianluca Ambrosi, Paolo Dapporto, Mauro Formica, Vieri Fusi, Luca Giorgi, Annalisa Guerri, Mauro Micheloni, Paola Paoli, Roberto Pontellini, Patrizia Rossi,

Chemical Reaction Mechanisms

The synthesis and characterization of two new macrocyclic ligands, the bis-macrocyclic compound 2,6-bis(1,4,13-triaza-7,10-dioxacyclopentadec-1-ylmethyl)phenol (L) and 38-methoxy-1,4,13,16,19,28-hexaaza-7,10,22,25-tetraoxatricyclo[14.14.7.132,36]octatriconta-32,34,Δ36,38-triene (L1) are reported. Equilibrium studies of basicity and coordination properties toward metal ions such as Cu(II), Zn(II), Cd(II) and Pb(II) were performed for ligand L by potentiometric measurements in aqueous solution (298.1 ± 0.1 K, I = 0.15 mol dm−3). L behaves as a hexaprotic base (logK1 = 10.93, logK2 = 9.70, logK3 = 8.79, logK4 = 8.05, logK5 = 6.83, logK6 = 2.55). All metal ions form stable mono- and dinuclear complexes: logKMLH−1 = 25.61 for Cu(II), 15.37 for Zn(II), 12.58 for Cd(II) and 13.79 for Pb(II); logKM2LH−1 = 31.61 for Cu(II), 23.38 for Zn(II), 24.49 for Cd(II) and 23.68 for Pb(II). All these dinuclear species show a great tendency to add the OH− group: the equilibrium constant for the addition reaction was found to be logKM2LH−1OH = 4.77 for Cu(II), 5.66 for Zn(II), 2.8 for Cd(II) and 3.18 for Pb(II). In the case of Ni(II), kinetic inertness prevents the possibility of solution studies. The dinuclear solid adducts [Ni2H−1L(N3)3]·EtOH and [Cu2H−1L(N3)](ClO4)2 were characterized by X-ray analysis.