Spectroscopic and Quantum Chemical Evidence of Amine-CO and Alcohol-CO Interactions: Confirming an Intriguing Affinity of CO to Monoethanolamine (MEA).

A recent broadband rotational spectroscopic investigation of the cross-association mechanisms of CO with monoethanolamine (MEA) in molecular beams [F. Xie et al., , , , e202218539] revealed an intriguing affinity of CO to the hydroxy group. These findings have triggered the present systematic vibrational spectroscopic exploration of weakly bound amine··CO and alcohol··CO van der Waals cluster molecules embedded in inert "quantum" matrices of neon at 4.2 K complemented by high-level quantum chemical conformational analyses. The non-covalent interactions formed between the amino and hydroxy groups and the electron-deficient carbon atom of CO are demonstrated to lift the degeneracy of the doubly degenerate intramolecular CO-bending fundamental significantly with characteristic observed spectral splittings for the amine··CO (≈35-45 cm) and alcohol··CO (≈20-25 cm) interactions, respectively, despite the almost identically predicted total association energies (≈12-14 kJ·mol) for these van der Waals contacts, as revealed by benchmark Domain-based Local Pair Natural Orbital Coupled Cluster DLPNO-CCSD(T) theory. These high-level theoretical predictions reveal significantly higher "geometry preparation energies" for the amine··CO systems leading to a more severe distortion of the CO linearity upon complexation in agreement with the infrared spectroscopic findings. The systematic combined spectroscopic and quantum chemical evidences for cross-association between CO and amines/alcohols in the present work unambiguously confirm an intriguing binding preference of CO to the hydroxy group of the important carbon capture agent MEA, with an accurate vibrational zero-point energy corrected association energy () of 13.5 kJ·mol at the benchmark DLPNO-CCSD(T)/aug-cc-pV5Z level of theory.