Competition between H2O and CH3OH molecules in the formation of the simplest stable proton disolvates and their solvation in aqueous methanol solutions of KOH and CH3OK

Resumo

IR spectroscopic and quantum chemical methods are used to study the competition between water and methanol molecules in the formation of the simplest stable proton disolvates and their subsequent solvation in the case of solutions of KOH in CH₃OH and CH₃OK in H₂O with similar stoichiometries (~1:3-3.5). The complexes found in these solutions are analysed to determine their composition and structure: they are found to be heteroions (CH₃O⋯H⋯OH)^– solvated by two similar solvent molecules. In both cases, there are virtually no complexes of the second possible type (CH₃OH·(CH₃O⋯H⋯OCH₃)^–··H₂O or CH₃OH·(HO⋯H⋯OH)^–·H₂O), which appears to be due to the stoichiometric compositions of the solutions. It is shown that a DFT calculation (B3LYP/6-31++G(d,p)) of linear complexes with strong (~15-30 kcal/mol) H bonds reproduces, with good accuracy, the IR spectra of the solutions, which consist mainly of these complexes.