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Chemistry ; 12(6): 1790-6, 2006 Feb 08.
Artigo em Inglês | MEDLINE | ID: mdl-16331709


Density functional calculations for [M(CH3)F5], [M(CF3)F5], [M(CH3S)F5], and [M(CF3S)F5] (M=Mo, W) show that they are expected to be nonrigid molecules, with energy barriers for the octahedral-trigonal-prismatic interchange as low as 7.2 kJ mol(-1). The ground state for the CH3- and CF3- compounds is trigonal prismatic, for the CH3S- and CF3S- compounds, (distorted) octahedral. All calculated compounds [M(C6F5)nF(6-n)] (M=Mo, W) have a trigonal-prismatic ground state, whereas the situation for [M(C6H5)nF(6-n)] (M=Mo, W) is more complex.

J Am Chem Soc ; 127(32): 11497-504, 2005 Aug 17.
Artigo em Inglês | MEDLINE | ID: mdl-16089480


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.

Chemistry ; 10(19): 4755-62, 2004 Oct 04.
Artigo em Inglês | MEDLINE | ID: mdl-15372575


Calculations reveal that the octahedral-trigonal prismatic-octahedral rearrangement has particularly low-energy barriers for MoF6, WF6, and (hypothetical) CrF6. Experimental evidence is obtained from the dynamic 19F NMR spectra of the derivatives CF3-CH2-O-MoF5, CF3-CH2-O-WF5, C6F5-O-MoF5, C6F5-O-WF5, and (CF3)3C-O-WF5. The ground-state structure of all these compounds is octahedral; at elevated temperatures the nonequivalent metal-bound fluorine atoms undergo an intramolecular exchange. The exchange mechanism could be a 3+3 or a 2+4 twist; calculations favor the 3+3 twist.