NEW MULTI-DENTATE LIGANDS .18. SYNTHESIS OF 1,4-BIS(BIS(2-AMINOETHYL)AMINOMETHYL)BENZENE - BINUCLEAR CHELATING TENDENCIES AND MIXED-LIGAND BINUCLEAR CHELATE FORMATION

The synthesis of l, 4-bis(bis(2-aminoethyl)aminomethyl)benzene hexahydrochloride (PXBDE) and the aqueous solution equilibria of this new hexadentate ligand with Cu(II), Ni(II), Co(II), and Zn(II) in both the presence and the absence of auxiliary bidentate ligands are described. At 25 °C and 0.10 M ionic strength, the protonation constants for PXBDE are 10.06, 9.71, 9.11, 8.57, 1.8, and 1.2 log units. The log K values of the 1:1 metal chelate stability constants (K = [MH2L]/[M][H2L]) are 13.21, 9.20, 6.84, and 7.19 with the above metals, respectively. For some metal ions at higher pH less protonated forms of the metal chelate, MHL3+ and ML2+, are also found. ML2+ reacts with excess metal ion to form a binuclear complex (M2L4+), while in <0.001 M solutions excess PXBDE fails to form a 1:2 metal-ligand complex with any of the above metal ions. PXBDE was found to form mixed-ligand complexes in the presence of metal ions and such bidentate ligands as ethylenediamine and glycine. The logarithms of the equilibrium formation constants for the most fully coordinated glycine species, β = [M2L‘2L]/[M]2[L‘]2[L], where L‘ = glycine, L = PXBDE, and M = Cu(II), Ni(II), Co(II), or Zn(II), are 37.96, 30.16, 23.38, and 25.56, respectively. Similarly when L‘ = ethylenediamine, the corresponding constants are 40.18, 31.68, 23.32, and 27.08. The probable arrangements of the coordination sites in the complexes studied and possible applications of the mixed-ligand systems are discussed. © 1979, American Chemical Society. All rights reserved.