The structure of benzonitrile-water complex as unveiled by matrix isolation infrared spectroscopy: Is it linear or cyclic at low temperatures?

Abstract

The hydrogen bonded interaction of benzonitrile (C6H5CN)-water (H2O) complexes have been studied experimentally using matrix isolation infrared spectroscopy to elucidate the structure(s) of the binary complexes produced at low temperatures. Computations performed at MP2 and B3LYP-D3 level of theory with aug-cc-pVDZ basis set predicted two complexes, of which global minimum complex A has a cyclic structure with the interactions occurring between ortho-hydrogen of C6H5CN and oxygen of H2O and the hydrogen of H2O with π-cloud of CN in C6H5CN. The linear acylic complex B, a local minimum is stabilized through a straight C-H⋯N interaction between nitrogen of C6H5CN and hydrogen of H2O and is present at a relative energy of ∼0.7 kcal/mol with respect to global minimum. While previous gas phase studies using a number of spectroscopic probes identify exclusively the cyclic global complex, our experiments performed under isolated conditions at low temperatures uniquely produced the acyclic linear C6H5CN-H2O complex, a local minimum in the potential energy surface. The CN stretching vibrational mode of C6H5CN was exploited as a unique marker to confirm the generation of local minimum. The effect of matrixes was simulated using Onsager self-consistent reaction field model and as a result, the linear complex (complex B) turned out to be energetically favored isomer under the influence of matrixes. The hydrogen bonding interaction in both the complexes was characterized using Atoms in Molecules, Natural Bond Orbital, Energy Decomposition and Non-Covalent Interaction analyses.