title: Jahn-Teller distortion in polyoligomeric silsesquioxane (POSS) cations.
abstract: We investigated the symmetry breaking mechanism in cubic octa-tert-butyl silsesquioxane and octachloro silsesquioxane monocations (Si8O12(C(CH3)3)8(+) and Si8O12Cl8(+)) using density functional theory (DFT) and group theory. Under Oh symmetry, these ions possess (2)T2g and (2)Eg electronic states and undergo different symmetry breaking mechanisms. The ground states of Si8O12(C(CH3)3)8(+) and Si8O12Cl8(+) belong to the C3v and D4h point groups and are characterized by Jahn-Teller stabilization energies of 3959 and 1328 cm(-1), respectively, at the B3LYP/def2-SVP level of theory. The symmetry distortion mechanism in Si8O12Cl8(+) is Jahn-Teller type, whereas in Si8O12(C(CH3)3)8(+) the distortion is a combination of both Jahn-Teller and pseudo-Jahn-Teller effects. The distortion force acting in Si8O12(C(CH3)3)8(+) is mainly localized on one Si-(tert-butyl) group, while in Si8O12Cl8(+) it is distributed over the oxygen atoms. The main distortion forces acting on the Si8O12 core arise from the coupling between the electronic state and the vibrational modes, identified as 9t2g + 1eg + 3a2u for the Si8O12(C(CH3)3)8(+) and 1eg + 2eg for Si8O12Cl8(+).
authors.affiliation: †Department of Chemistry, University of Richmond, Richmond, Virginia 23173, United States.
authors.forename: Jules
authors.initials: J
authors.lastname: Tshishimbi Muya
authors.affiliation: ‡Department of Chemistry, University of Leuven, Celestijnenlaan 200F, Heverlee, B-3001, Belgium.
authors.forename: Arnout
authors.initials: A
authors.lastname: Ceulemans
authors.affiliation: §Fuel Chemistry Division, Indira Gandhi Centre for Atomic Research, Kalpakkam, Tamilnadu 603102, India.|∥Max-Planck Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, Mülheim an der Ruhr, 45470, Germany.
authors.forename: Gopinadhanpillai
authors.initials: G
authors.lastname: Gopakumar
authors.affiliation: †Department of Chemistry, University of Richmond, Richmond, Virginia 23173, United States.
authors.forename: Carol A
authors.initials: CA
authors.lastname: Parish