A spectrophotometric study of the system: cobalt--2,2,8,8-tetrakis (hydroxymethyl)-3,7-diaza-1,5,9-nonanetriol

Spectrophotometric studies or solutions or 2,2;8;a. tetrakis(hydroxymethyl)-3, 7-diaza-1,5.9-nonanetriol, (HOCH2),3CHNCH2CH(OH)CH2NHC(CH2OH)3, with cobalt (II) gave evidence of complexes having metal-ligand ratios of 1:2 and 1:3. Complexation appeared nearly complete at pH 8 or greater. Between pH 8 and pH 11, the positions of the maxima in the absorbance spectra remained essentially constant and no precipitation was observed. The 1:2 complex formed rapidly, while the 1:3 complex formed more slowly, requiring one to two weeks to reach equilibrium, after which the solutions remained unchanged over a period or several months. Evidence of the 1:2 complex was obtained using the elope-ratio (32) within one hour of the initial mixing. At later times, precipitation in the solutions containing high relative metal concentrations inhibited measurement. Attempts to prepare analogous cobalt (m) complexes were unsuccessful. Modification of the method or Laitinen and Burdett produced solutions whose spectra changed so rapidly that the changes could be observed while the solutions were being measured. Precipitation followed within two to three hours. The complexes of 2,2,8,8-tetramethyl-3, 7-diaza-5-nonanol (CH3)3CNHCH2CH(OH)CH2NHC(CH3)3, appeared so unstable under the experimental conditions that even at high ligand ratios precipitation of the hydroxide occurred and measurements could not be made