Complex Formation between M(II) (M=Cu, Zn, Mn) and 2- (5-Bromo-2-pyridylazo) -5- (N-propyl-N-3-sulfopropylamino) phenol

Abstract

Complex formation (1:1) between M (M = Cu, Zn, Mn) and 2- (5-bromo-2-pyridylazo) -5- (NpropylN-3-sulfopropylamino) phenol (5-Br-PAPS) has been studied by spectrophotometry at 25°C and at 1= 0.1 (NaNO₃). The protonated complex, MHL, is found to exist in equilibrium with the normal complex, ML, at pH 1-2 for Cu (II) and pH 4-5 for Zn(II). The ML complex is only formed for Mn(II)at pH > 6.5. The formation constants KMLa nd ICMHaLr e obtained by a graphical analysis. Comparison of the KML values obtained with those for the complexes having similar structure showed that the stability of the ML complexes is governed by the basicity of the oxygen atom ortho to the azo group but not affected by the other substituent in the para or meta position. The values of Kmm, obtained are found to be much smaller than those of the PAR complexes.