An infrared spectroscopic study of the hydration of the triflate ion (CF3SO−3) in aqueous solution

The hydration of the trifluoromethanesulphonate ion (triflate ion) in aqueous solution has been studied using infrared spectroscopy. A double difference technique has been applied to an aqueous solution of 0.463 M Ni (CF3SO3)2. The OD stretching spectrum of isotopically diluted HDO molecules in the hydration spheres of the ions was obtained. The triflate ion hydration band is positioned at 2605±1 cm−1 with a total bandwidth at half height of 85±2 cm−1. A coordination number of 1.5±0.9 is found for the triflate ion. Spectra in the CF and SO stretching region are presented for aqueous solutions of 0.5 M Ba(CF3SO3)2 and 0.5 M Ni(CF3SO3)2, as well as for the solid hydrate La(CF3SO3)3·9H2O. The OD stretching spectrum of partially deuterated (5% HDO) solid lanthanum nonahydrate is also presented; three peaks are observed at 2529, 2548 and 2585 cm−1. An extraordinarily high average OH stretching frequency of 3656 cm−1 is found for residual water molecules in the dried solid lanthanum hydrate. The hydration characteristics of the triflate ion in aqueous solution are discussed on the basis of the infrared spectroscopic results. It is concluded that the triflate ion is only involved in hydrogen bonding at its SO3 end, and that water molecules in the vicinity of the CF3 end are not spectroscopically distinguishable from bulk water.