An ESR Study of Mn(II) Complexes in Water-Methanol Mixed Solvents

Abstract

0.01 ᴍ solutions of Mn (ClO4)2, MnCl2 and MnSO4 in water-methanol mixtures were studied at 25 °C to determine the effect of these anions and of solvent composition on the ESR intensity and linewidth of Mn(II). A significant feature of the data was the large difference between the intensity of Mn(ClO4)2 and that for MnCl2 and MnSO4 in solutions containing greater than about 0.5 mole fraction methanol. A plot of linewidth versus mole fraction methanol shows little difference between Mn(ClO4)2 and MnCl2 but an increasingly greater difference between these salts and MnSO4 with increasing methanol content. These results are interpreted as being due to first coordination sphere complex formation in solutions containing Cl⊖, while the SO4 2⊖ data are affected by both first and second coordination sphere complexes depending upon the solvent dielectric constant. The Mn(ClO4)2 data were interpreted as showing that the primary solvation sphere of the Mn(II) ions was changing as the composition of the bulk solvent changed. These results are compared with similar data in aqueous solution and confirm that complex formation involving Cl⊖ or SO4 2⊖ ions and Mn(II) is extensive in water-methanol mixtures.