1:2 Formic Acid/Acetylene Complexes: Ab Initio and Matrix Isolation Studies of Weakly Interacting Systems

Abstract

The complexes formed by noncovalent interactions between one molecule of formic acid and two molecules of acetylene are investigated by DFT and ab initio methods and characterized by matrix isolation spectroscopy. Six complexes with binding energies between −3.93 and −7.98 kcal/mol (MP2/cc-pVTZ + ZPE) are identified. The three most strongly bound complexes are found within a range of 1 kcal/mol. The binding interactions in these complexes are OH···π, CH···π, and CH···O interactions that can be classified as weak hydrogen bonds. The competition between these weak hydrogen bonds is discussed in detail. Matrix isolation spectroscopy allowed for the characterization of the most strongly bound complex by its IR spectrum.