Formation of cobalt(II), nickel(II) and copper(II) chloro complexes in alcohols and the Irving-Williams order of stabilities

Summary Co^II chloro complexes were studied in MeOH at 25 °C and at constant ionic strength of 1 mol dm^–3. Formation of three complexes is postulated for which the overall stability constants are calculated: log ₁ = 1.2, log ₂ = 1.7 and log ₃ = 1.4. The electronic spectra and the formation curves of the identified species are presented for the first time in this medium. The results are compared with those obtained in other alcohols and increasing stability with increasing molecular weight of the solvents is established. Further comparative study showed that the maximum stability of the chloro complexes is found with the Cu^II ion as the central atom. This confirms the Irving-Williams order of stabilities for the first transition metal complexes in this alcoholic medium and the result is explained in terms of the second ionization potential of the elements.