Complex formation in methanol-chloroform solutions:Vibrational spectroscopy and quantum cluster equilibrium study

Methanol-chloroform solutions with different mixing ratios were studied using vibrational (ATR FTIR and Raman) spectroscopy. Obtained spectra were analyzed by different techniques such as excess spectroscopy and multivariate curve resolution. Analysis of vibrational spectra showed that the investigated solutions consist of four kinds of species: ‘pure’ methanol, ‘pure’ chloroform, and two types of ‘effective’ molecular complexes. Molecular complexes were present in the entire concentration range of methanol dilutions in chloroform. Obtained spectral profiles of ‘pure’ methanol and ‘pure’ chloroform were identical to spectra of bulk species which means that their structure in solution is similar to corresponding ones in bulk methanol and chloroform. Minimal sets of possible structures of associates and molecular complexes were calculated using density functional theory. Information about optimized structures was further used for quantum cluster equilibrium (QCE) calculations. These calculations allowed us to explain the concentration dependence of excess enthalpy of methanol-chloroform solution. It was demonstrated that obtained concentrations of mixture components correlate with experimental ones obtained by MCR-ALS.