Disruption of Hydrogen Bond Networks by Organic Salts

High concentrations of salts, for example, in electrochemical double layers, affect solvation and local electrostatics and can disrupt the hydrogen bonding networks (HBNs). To investigate the effects of salts on the HBNs, we added the organic salt tetrabutylammonium hexafluorophosphate (TBA + PF 6 – ) to hexafluoroisopropanol (HFIP), which is a strong hydrogen bond donor and a weak hydrogen bond acceptor and, therefore, can form HBNs. We used propionitrile (EtCN), acetonitrile (MeCN), and methyl thiocyanate (MeSCN) as vibrational reporters of hydrogen bonding and monitored their Raman spectra in salt solutions of varying concentrations. We observed that the frequencies of the probes red shifted significantly from pure HFIP to 2.5 M TBA + PF 6 – solution in HFIP, indicating disruption of HBNs by the salt. We performed control experiments in DMSO to isolate the electrostatic or solvation field effects of the salts. Our finding implies that a high concentration of organic salts reduces the reactivity of hydrogen bonds and may impede proton transfer reactions, thereby requiring fine-tuning of reactivity in high salt environments.