Two triaza-polyamine units linked together by different aromatic spacers, coordination properties towards metal cations of a new compartmental ligand

The synthesis of the flexible ligand 2,6-bis-{[bis-(2-aminoethyl)amino]methyl}-benzene (L1) is reported. The basicity behavior of the ligand in aqueous solution was studied by potentiometry (25 degreesC,I=0.15 mol dm(-3), Me4NCl). L1 behaves as pentaprotic base (log K-1 = 10.39(2), log K-2 = 9.72(1), log K-3 = 9.11(1), log K-4 = 8.72(1), log K-5 = 2.03(2)). The stability constants for Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Pb(II) complexes were determined by potentiometry under the same experimental conditions and they were compared with those of ligands L2 having the same two tri-amine subunits linked by a phenol, rather than a benzene, spacer. L1 forms mono nuclear species with log K-ML = 9.65(1) for Co(II), 13.92(1) for Ni(II), 17.59(1) for Cu(II), 10.45(1) for Zn(II) and 9.24(1) for Cd(II) and binuclear species with log K-M2L = 15.28(1) for Co(II), 19.24(3) for Ni(II), 28.32(2) for Cu(II), 16.94(1) for Zn(II) and 14.88(1) for Cd(II). The role of the benzene and phenol as spacers of two amine functions in metal ion coordination is discussed. (C) 2002 Elsevier Science Ltd. All rights reserved.