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

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 center dot center dot center dot H center dot center dot center dot O(H)Et)(+) and (Et(H)O center dot center dot center dot H center dot center dot center dot O(H)Et)(+) with the quasi-symmetrical O center dot center dot center dot H+center dot center dot center dot O unit having O center dot center dot center dot O separation <2.45 angstrom 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 center dot center dot center dot H+center dot center dot center dot Cl- complex exists. Copyright (c) 2013 John Wiley & Sons, Ltd.