Revealing pre-catalytic CO2 recognition in styrene oxide complexes via rotational spectroscopy.

High-resolution rotational spectroscopy combined with quantum chemical calculations was employed to investigate the non-covalent interactions between styrene oxide and carbon dioxide. Four low-energy complex isomers were predicted, among which the global minimum was experimentally identified through agreement between theoretical and measured rotational constants. The phenyl substituent was found to introduce additional non-covalent interactions beyond the typical CCO2⋯O tetrel bond, including secondary C⋯OCO2 tetrel bond and C-H⋯OCO2 weak hydrogen bond, which collectively stabilized the complex and distorted the epoxide ring. Further π-electron localization and natural orbital for chemical valence analyses revealed that the phenyl ring modulated local electron density, while comparative calculations of binding energy further indicate that the synergistic weak interactions between styrene oxide and CO2 contribute to enhancing the structural stability of the styrene oxide-CO2 complex. These results shed light on substituent-controlled CO2 recognition in epoxide frameworks, offering molecular-level insight that may inform the design of functional materials for CO2 capture and chemical transformation.