Complexation of copper(II) with 3-(2-hydroxyphenylazo)pentadione-2,4

It is shown that 3-(2-hydroxyphenylazo)pentadione-2,4 (H₂L) can exist in three tautomeric forms (enol-azo, keto-azo, and hydrazo). The effective atomic charges in the tautomeric forms of H₂L are calculated by the Hückel MO LCAO method. The molar fractions and molar absorptivities of the tautomers at different pH are found. The complexation of copper(II) with H₂L is studied by spectrophotometry. Beer’s law is obeyed for 0.51–5.12 µg/mL of copper. The assumed complex structure is given. The effect of foreign ions and masking agents on the complexation is studied. A procedure for the photometric determination of copper(II) in zinc-based alloys is proposed.