Influence of alkali cations on the infrared spectra of water molecules in aprotic solvents

Abstract

The influence of alkali cations on the frequency of the OH vibration of H-bonded HOD (or H/sub 2/O) in dilute ternary mixtures (salt/water/aprotic solvent with H-bond acceptor groups B) is observed. The authors find that the magnitude of the frequency shift due to the cation increases proportionally with the frequency shift due to the O-H...B H bond in the dilute binary (water/solvent) mixture. The correlation between OH-frequency shifts in different solvents (OH...B complexes) and the additional shift due to Li/sup +/, Na/sup +/, and K/sup +/ salts is linear. The slopes of these correlations may be taken as a measure of the cooperative influence of the cations. The slopes are Li/sup +/, 0.55; Na/sup +/, 0.40; K/sup +/, approx. 0.08. Some possible consequences of this cooperativity on H-bond energies, enthalpies of solutions, and O-O distances in aqueous salt solutions are discussed.