The structure and vibrational features of proton disolvates in water-ethanol solutions of HCl: the combined spectroscopic and theoretical study

Abstract

The infrared (IR) spectra of water–ethanol (EtOH) solutions of HCl are measured over a wide range of acid concentration at fixed H2O―EtOH ratios (1 : 1, 1 : 2, and 1 : 40). In these systems, different proton disolvates with (quasi)symmetrical H-bonds are formed. Their structure and vibrational features are revealed by the density functional theory method coupled with the polarizable continuum model of solvation. In dilute acidic solutions, the Zundel-type H5O2+ ion is mainly formed. In concentrated HCl solutions, the ions (H2O···H···O(H)Et)+ and (Et(H)O···H···O(H)Et)+ with the quasi-symmetrical O···H+···O unit having O···O separation <2.45 A appear. The first ion characterized by the IR-intensive band around 1800 cm−1 is mainly formed in the 1 : 1 water–ethanol systems. The second ion exists in the 1 : 2 and 1 : 40 water–ethanol systems. Its spectroscopic signatures are the groups of the IR-intensive bands around 800 and 1050 cm−1. In highly concentrated HCl solutions with the 1 : 40 water–ethanol ratio, a neutral Et(H)O···H+···Cl− complex exists. Copyright © 2013 John Wiley & Sons, Ltd.