Potentiometric and conductometric studies on some diphenyformazans and their metal chelates

The ACID dissociation constant pKa values of 1-aryl-5 -[o- hydroxybenzene]-3-benzoylformazan derivatives in ethanol- water mixtures have been determined pH-metrically at 25 +/- 0.2 degree. Increase in the concentration of ethanol results in the increase of pK for all formazan derivatives. The formation constant log kMML values of some lanthanide complexes were determined in 70% [v/v] ethanol. The potentiometric and conductometric studies revealed that 1: 1 and 1: 2 [metal: ligand] complexes were formed in solution. The correlation of the stability constants of complexes in relation to ionic radii, ionic potential and electronegativity of the lanthanides was discussed