Density functional theory study of interactions between carbon dioxide and functionalized polyhedral oligomeric silsesquioxanes

摘要

Polyhedral Oligomeric Silsesquioxanes (POSS) are cage-structured inorganic-organic hybrid materials which can be used in various industrial applications. It is recently discovered that POSS structures with certain functional groups can be solubilized in supercritical CO2 allowing their applications in environmentally benign supercritical processing of materials. In this theoretical study, nature and energetics of the interactions of octatrifluoropropyl POSS, octatrifluoromethyl POSS, and octamethyl POSS with CO2 are investigated according to the principles of density functional theory (DFT) by use of Gaussian 09 software. Simulations show that CO2-octamethyl POSS pair has hydrogen bonding between the O atom of CO2 and the H atom of the methyl group, and CO2-octatrifluoromethyl POSS pair has interactions between the C atom of CO2 and the F atom of the trifluoromethyl group. CO2-octatrifluoropropyl POSS pair is found to have both interaction types. The octamethyl, the octatrifluoromethyl and the octatrifluoropropyl POSS structures have interaction energies of -22.18kcal/mol, 23.10 kcal/mol, and 23.77 kcal/mol, respectively. This shows that the presence of Lewis acid-Lewis base interaction between C and F instead of hydrogen bonding between O and H atoms enhances the interaction of the molecule with CO2, while the presence of both interactions between the octatrifluoropropyl POSS-CO2 pair makes the intermolecular interaction even stronger.