Calculation of 19F and 29Si NMR Shifts and Stabilities of F- Encapsulating Silsesquioxanes

摘要: Hartree−Fock and density functional theory techniques have been used to calculate the structures, stabilities in aqueous toluene solutions, 19F 29Si NMR shifts of F- encapsulating double-ring geometry silsesquixoanes DnR with n = 3−6. We find for fluorides that encapsulation free energy is most negative double four-ring (D4R) cage, which stable has center. For 5, 6 (and an opened version five-ring, D5R, cage), bonded a single apex Si atom, bond distance around 1.76 A. The somewhat deshielded relative Si(OH)4F- monomer all species very strongly central 3, 4. slightly by presence ions, while apex-bonded larger rings, 6, directly substantially shielded. ene...