Synthesis, Spectroscopic and Electrochemical Characterization, and DFT Study of Seventeen C₇₀(CF₃)_n Derivatives (n=2, 4, 6, 8, 10, 12)

Abstract

Eight new C70(CF3)n derivatives (n=2, 6, 10, 12) have been synthesized and characterized by UV/Vis and 19F NMR spectroscopy, cyclic voltammetry, and quantum chemical calculations at the DFT level of theory. Nine previously known derivatives of C70(CF3)n with n=2-12 were also studied by cyclic voltammetry (and seven of them by UV/Vis spectroscopy for the first time). Most of the 17 compounds exhibited two or three reversible reductions at scan rates from 20 mV s(-1) up to 5.0 V s(-1). In general, reduction potentials for the 0/- couple are shifted anodically relative to the C70 0/-) couple. However, the 0/- E1/2 values for a given composition are strongly dependent on the addition pattern of the CF3 groups. The data show that the addition pattern is as important, if not more important in some cases, than the number of substituents, n, in determining E1/2 values. An analysis of the DFT-predicted LUMOs indicates that addition patterns that have non-terminal double bonds in pentagons result in derivatives that are strong electron acceptors.

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

“…The CF 2 region of the 19 F NMR spectrum shown in Figure 1 is therefore a second-order ABCD pattern averaged over the four conformations shown in Figure 3 Figure 4 (the voltammograms for 7,24-and 8,23-C 70 A C H T U N G T R E N N U N G (CF 3 ) 2 were recently reported [19] ). Both 7,24-C 70 (R f ) 2 compounds exhibit three reversible one-electron reductions in dichloromethane at a scan rate of 20 mV s Table 1.…”

“…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.…”

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

“…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. For example, only one addition pattern is common for six known (or suggested) isomers of C 70 -(CF 3 ) 10 [2,7] and seven known isomers of C 70 (C 2 F 5 ) 10 . [6] One can therefore assume that even larger fluoroalkyl groups would produce derivatives with new addition patterns.…”

“…[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.…”

New isomers of trifluoromethylated fullerene: C60(CF3)12 and C60(CF3)14

“…6,7 It should be noted that the process of trifluoromethyla tion of fullerenes is sensitive to small variations of syn thesis conditions such as temperature, pressure of the re agent, reaction time, and even the shape of the reaction ampoules, which can affect isomeric composition of the reaction product. 6, 8 Only the C 60 (CF 3 ) 12 I isomer with molecular symmetry S 6 can be synthesized with high selec tivity. 6 Its separation from other trifluoromethylated fullerenes can be easily accomplished because the crystal line form of this isomer obtained in the synthesis is poorly soluble in organic solvents.…”