title: Variable-temperature 19F NMR and theoretical study of 1,9- and 1,7-C60F(CF3) and C(s-) and C1-C60F17(CF3): hindered CF3 rotation and through-space J(FF) coupling.
abstract: Milligram amounts of the new compounds 1,9- and 1,7-C60F(CF3) (ca. 85:15 mixture of isomers) and C60F3(CF3) were isolated from a high-temperature C60/K2PtF6 reaction mixture and purified to 98 mol % compositional purity by two-dimensional high-performance liquid chromatography using Buckyprep and Buckyclutcher columns. The previously observed compounds C60F5(CF3) and C60F7(CF3) were also purified to 90+ mol % for the first time. Variable-temperature 19F NMR spectra of the mixture of C60F(CF3) isomers and the previously reported mixture of C(s)- and C1-C60F17(CF3) isomers demonstrate for the first time that fullerene(F)n(CF3)m derivatives with adjacent F and CF3 substituents exhibit slow-exchange limit hindered CF3 rotation spectra at -40 +/- 10 degrees C. The experimental and density functional theory (DFT) predicted deltaH++ values for CF3 rotation in 1,9-C60F(CF3) are 46.8(7) and 46 kJ mol(-1), respectively. The DFT-predicted deltaH++ values for 1,7-C60F(CF3), C(s)-C60F17(CF3), and C1-C60F17(CF3) are 20, 44, and 54 kJ mol(-1), respectively. The (> or = 4)J(FF) values from the slow-exchange-limit 19F spectra, which vary from ca. 0 to 48(1) Hz, show that the dominant nuclear spin-spin coupling mechanism is through-space coupling (i.e., direct overlap of fluorine atom lone-pair orbitals) rather than coupling through the sigma-bond framework. The 2J(FF) values within the CF3 groups vary from 107(1) to 126(1) Hz. Collectively, the NMR data provide an unambiguous set of (> or = 4)J(FF) values for three different compounds that can be correlated with DFT-predicted or X-ray diffraction derived distances and angles and an unambiguous set of 2J(FF) values that can serve as an internal standard for all future J(FF) calculations.
authors.affiliation: Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka 142432 Russia.
authors.forename: Ivan E
authors.initials: IE
authors.lastname: Kareev
authors.forename: Gustavo Santiso
authors.initials: GS
authors.lastname: Quiñones
authors.forename: Igor V
authors.initials: IV
authors.lastname: Kuvychko
authors.forename: Pavel A
authors.initials: PA
authors.lastname: Khavrel
authors.forename: Ilya N
authors.initials: IN
authors.lastname: Ioffe
authors.forename: Ilya V
authors.initials: IV
authors.lastname: Goldt
authors.forename: Sergey F
authors.initials: SF
authors.lastname: Lebedkin
authors.forename: Konrad
authors.initials: K
authors.lastname: Seppelt
authors.forename: Steven H
authors.initials: SH
authors.lastname: Strauss
authors.forename: Olga V
authors.initials: OV
authors.lastname: Boltalina