Complexes of copper(I) with aromatic compounds in aqueous solutions

The apparent stability constants of the complexes of Cu+(aq) with several a romatic compounds, mainly substituted benzoic acids, were determined electr ochemically. The results reveal that these complexes are surprisingly stabl e, 2.0 less than or equal to log K less than or equal to 4.0 at the pK(a) o f the benzoic acids. The stability constants depend on the pH. This depende nce is considerably stronger than that predicted from the pK(a) of the acid s, suggesting that complexes of CuOH with the aromatic acids are also forme d. Electron donating substituents increase the apparent stability constants . The results indicate that the complexes formed are due to d --> pi intera ctions between the copper d orbitals and the aromatic pi system. The effect of Cu+(aq) on the H-1 NMR of benzoic acid supports this conclusion.