The Existence of
In this study, 16 gas phase complexes of the pairs of XCHZ and CO(2) (X = F, Cl, Br; Z = O, S) have been identified. Interaction energies calculated at the CCSD(T)/aug-cc-pVTZ//MP2/aug-cc-pVTZ level including both BSSE and ZPE corrections range from -5.6 to -10.5 kJ mol(-1) for XCHOCO(2) and from -5.7 to -9.1 kJ mol(-1) for XCHSCO(2). Substitution of one H atom by one halogen in formaldehyde and thioformaldehyde reduces the interaction energy of XCHZCO(2), while a CH(3) substitution increases the interaction energy of both CH(3)CHOCO(2) and CH(3)CHSCO(2). NBO and AIM analyses also point out that the strength of Lewis acid-base interactions decreases going from >C1double bond, length as m-dashS3C6 to >C1double bond, length as m-dashO3C6 and to >C1-X4C6. This result suggests the higher capacity of solubility of thiocarbonyl compounds in scCO(2), providing an enormous potential application for designing CO(2)-philic materials based on the >Cdouble bond, length as m-dashS functional group in competition with >Cdouble bond, length as m-dashO. The Lewis acid-base interaction of the types >Cdouble bond, length as m-dashSC, >C-ClC and >C-BrC is demonstrated for the first time. The contribution of the hydrogen bonding interaction to the total interaction energy is larger for XCHSCO(2) than for XCHOCO(2). Upon complexation, a contraction of the C1-H2 bond length and a blue shift of its stretching frequency have been observed, as compared to the isolated monomer, indicating the existence of a blue-shifting hydrogen bond in all complexes examined. Calculated results also lend further support for the viewpoint that when acting as proton donor, a C-H bond having a weaker polarization will induce a stronger distance contraction and frequency blue shift upon complexation, and vice versa.