Acetonitrile–water hydrogen-bonded interaction: Matrix-isolation infrared and ab initio computation

• Experimental evidence for the formation of linear 1:1 CH3CNH2O.
• Computation showed two minima a linear and cyclic complex.
• Computations were also carried out for 1:2 and 2:1 complexes of CH3CN and H2O.
• AIM and NBO analyses were carried out for the complexes A and B.

The 1:1 hydrogen-bonded complex of acetonitrile (CH3CN) and water (H2O) was trapped in Ar and N2 matrices and studied using infrared technique. Ab initio computations showed two types of complexes formed between CH3CN and H2O, a linear complex A with a CN⋯H interaction between nitrogen of CH3CN and hydrogen of H2O and a cyclic complex B, in which the interactions are between the hydrogen of CH3CN with oxygen of H2O and hydrogen of H2O with π cloud of CN of CH3CN. Vibrational wavenumber calculations revealed that both the complexes A and B were minima on the potential energy surface. Interaction energies computed at B3LYP/6-311++G(d,p) showed that linear complex A is more stable than cyclic complex B. Computations identified a blue shift of ∼11.5 cm−1 and a red shift of ∼6.5 cm−1 in the CN stretching mode for the complexes A and B, respectively. Experimentally, we observed a blue shift of ∼15.0 and ∼8.3 cm−1 in N2 and Ar matrices, respectively, in the CN stretching mode of CH3CN, which supports the formation of complex A. The Onsager Self Consistent Reaction Field (SCRF) model was used to explain the influence of matrices on the complexes A and B. To understand the nature of the interactions, Atoms in Molecules (AIM) and Natural Bond Orbital (NBO) analyses were carried out for the complexes A and B.