Potentiometric and spectrophotometric determination of the stabilities of In(III), Ga(III) and Fe(III) complexes of N,N′,N″-tris(3,5-dimethyl-2-hydroxybenzyl)-1,4,7-triazacyclononane
1991; Elsevier BV; Volume: 186; Issue: 1 Linguagem: Inglês
10.1016/s0020-1693(00)87938-4
ISSN1873-3255
AutoresEric T. Clarke, Arthur E. Martell,
Tópico(s)Electrochemical Analysis and Applications
ResumoThe protonation constants of potentially six-coordinate N,N′,N″-tris(3,5-dimethyl-2-hydroxybenzyl)-1,4,7- triazacyclononane (TX-TACN) were determined by spectrophotometric and potentiometric methods in 75% ethanol-25% water (μ=0.100 M (KCl), t=25.0 °C), and were found to be (log values) 14.2, 13.6, 12.9, 8.04 and 2.15. The stability constants of the complexes of In(III), Ga(III) and Fe(III) with TX-TACN were determined in the same medium by spectrophotometric methods, except for In(III)-TX-TACN, which was determined directly by potentiometric titration. The log stability constant for Fe(III)-TX-TACN (KML[ML]/[L3−][M3+]), determined by competition with EDTA in 75% ethanol-25% water is 51.3. The log stability constant for Fe(III)-EDTA (KML[ML−]/[L4−][M3+]) was found to be 26.3 in the same medium. The stability constants for the Ga(III) and In(III) complexes with TX-TACN are 1044.2 and 1033.99, respectively. The high stabilities of the Ga(III) and Fe(III) complexes with TX-TACN are rationalized on the basis of the close fit of these hexacoordinate metal ions in the ligand cavity formed by the pseudo-octahedral arrangement of ligand donor atoms: the basic nitrogen atoms of the macrocycle and the very basic phenolate oxygen atoms.
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