Synthesis, Characterization, and Theoretical Study of Stable Isomers of C₇₀(CF₃)_n (n = 2, 4, 6, 8, 10)

Abstract

Reaction of C70 with ten equivalents of silver(I) trifluoroacetate at 320-340 degrees C followed by fractional sublimation at 420-540 degrees C and HPLC processing led to the isolation of a single abundant isomer of C70(CF3)n for n = 2, 4, 6, and 10, and two abundant isomers of C70(CF3)8. These six compounds were characterized by using matrix-assisted laser desorption ionization (MALDI) mass spectrometry, 2D-COSY and/or 1D 19F NMR spectroscopy, and quantum-chemical calculations at the density functional theory (DFT) level. Some were also characterized by Raman spectroscopy. The addition patterns for the isolated compounds were unambiguously found to be C1-7,24-C70(CF3)2, C1-7,24,44,47-C70(CF3)4, C2-1,4,11,19,31,41-C70(CF3)6, Cs-1,4,11,19,31,41,51,64-C70(CF3)8, C2-1,4,11,19,31,41,51,60-C70(CF3)8, and C1-1,4,10,19,25,41,49,60,66,69-C70(CF3)10 (IUPAC numbering). Except for the last compound, which is identical to the recently reported, crystallographically characterized C70(CF3)10 derivative prepared by a different synthetic route, these compounds have not previously been shown to have the indicated addition patterns. The largest relative yield under an optimized set of reaction conditions was for the Cs isomer of C70(CF3)8 (ca. 30 mol % of the sublimed mixture of products based on HPLC integration). The results demonstrate that thermally stable C70(CF3)n isomers tend to have their CF3 groups arranged on isolated para-C6(CF3)2 hexagons and/or on a ribbon of edge-sharing meta- and/or para-C6(CF3)2 hexagons. For Cs- and C2-C70(CF3)8 and for C2-C70(CF3)6, the ribbons straddle the C70 equatorial belt; for C1-C70(CF3)4, the para-meta-para ribbon includes three polar hexagons; for C1-7,24-C70(CF3)2, the para-C6(CF3)2 hexagon includes one of the carbon atoms on a C70 polar pentagon. The 10.3-16.2 Hz 7JF,F NMR coupling constants for the end-of-ribbon CF3 groups, which are always para to their nearest-neighbor CF3 group, are consistent with through-space Fermi-contact interactions between the fluorine atoms of proximate, rapidly rotating CF3 groups.

ESR‐Vis/NIR Spectroelectrochemical Study of C70(CF3)2−. and C70(C2F5)2−. Radical Anions

“…Although multiple isomers of C 70 A C H T U N G T R E N N U N G (CF 3 ) 2 with a para-C 6 A C H T U N G T R E N N U N G (CF 3 ) 2 hexagon are possible, the only isomers of this composition isolated to date are the asymmetric isomer 7,24-C 70 A C H T U N G T R E N N U N G (CF 3 ) 2 [11] and the less abundant C s -symmetric isomer 8,23-C 70 A C H T U N G T R E N N U N G (CF 3 ) 2 [19] (see Supporting Information for the numbering scheme used in this paper). These compounds were minor components of a complex mixture of C 70 A C H T U N G T R E N N U N G (CF 3 ) n derivatives with n = 2, 4, 6, 8, and 10.…”

“…[11] In contrast, the addition of two C 8 F 17 radicals to La@C 82 at 25 8C resulted in the isolation of seven isomers of La@C 82 A C H T U N G T R E N N U N G (C 8 F 17 ) 2 . [27] The Dupont group of Fagan et al was the first to show that the addition of multiple R f radicals to C 70 leads to a wide range of compositions C 70 A C H T U N G T R E N N U N G (CF 3 ) n with even values of n from 2 to 14.…”

“…[6] However, similar results have not yet been reported for anions of C 70 (R f ) n compounds, and for this reason we have started an investigation of their spectroscopic properties. In this paper we report the synthesis of C 70 A C H T U N G T R E N N U N G (C 2 F 5 ) 2 , which was found to be isostructural to C 1 -7,24-C 70 A C H T U N G T R E N N U N G (CF 3 ) 2 , [11] and an ESR-Vis-NIR spectroelectrochemical study of both compounds.…”

Preparation, Crystallographic Characterization, and Theoretical Study of C70(CF3)14

“…The library of individual compounds thus obtained includes C 60 (CF 3 ) n with n = 2-10 [4] and C 70 (CF 3 ) m with m = 2-12. [5,6] Because of the small available amounts of these substances and other technical difficulties, however, only in a very few cases has it appeared feasible to go beyond a typical 19 F NMR characterization and to perform an X-ray crystallographic investigation: direct structural determination has so far been carried out only for C 60 -(CF 3 ) 10 , [4] C 70 (CF 3 ) 8 , [7] C 70 (CF 3 ) 10 , [8] and two isomers of tained are energetically favorable but that there is probably no full thermodynamic control in the trifluoromethylation process.…”

Synthesis and Structural Characterization of Four Isomers of C70(n‐C3F7)8

“…[1,2] The largest group of compounds is represented by trifluoromethyl derivatives, C 60/70 (CF 3 ) n , with n ranging from 2 to 18. [3,4] Among perfluoroethylated fullerenes, several representatives of C 60 (C 2 F 5 ) n (n = 6-10) [5] and C 70 (C 2 F 5 ) n (n = 10) [6] are known so far. Noteworthy, addition patterns of isolated pentafluoroethylated isomers seldom coincide with those of trifluoromethylated ones, which thus reveals an influence of the size of the perfluoroalkyl group on the relative stability of the isomers.…”