Ultraviolet Spectrophotometric Determination of the Compositions and the Stabilities of the α, α '-Ethylenediiminodi(ο -hydroxyphenylacetic acid) Complexes of Lead(II) and Copper (II)

Abstract

Compositions, stability constants, molar extinction coeMcients and stability pH ranges for lead(II)an, d coPPer(II)-complexes of, -ethylenediiminodi(o-hydroxyphenylacetic acid)(EHPG)have been determined spectrophotometrically.
The molar ratio of metal to ligand of each complex was 1: 1. On the basis of the absorption curves of the complexes of EHPG as well as ethylenediamine-N, N'-diacetic acid (EDDA)and the pH-absorbance curves, the following species would be assumed; firstly, doubly protonated chelate species MH2X, with two free phenolic hydroxyl groups, for lead(II)and copPer (II) at below pH's 6.0 and 3.6, respectively, and, secondly, at abeve these pH's a singly protonated and normal chelate species MHX, MX, with the metal-phenolate linkage, for both lead(II)and coppe: r(II).
The data observed were as follows; the logarithms of the stability constants at ionic strength O.10 adjusted with NaCIO' and 200C were 9.64, 14.57, 12.91, 20.15, 15.09 and 23.94 for PbH2X, CuH2X, PbHX, CuHX, PbX and CuX, respectively, the molar abserption coeMcients were 4.96 10S, 8.20 10S, 5.79 10S, 9.14 10S, 8.66 103 and 9.30 108 at the absorption maximum wavelengths of 273, 274, 280, 275, 292 and 292 nm, again respectively.