The X‐Ray Crystal Structures of a 1,9‐ and a 7,8‐Diels‐Alder monoadduct of C₇₀

Abstract

Accurate low-temperature X-ray crystal structures of the isomeric Diels-Alder monoadducts of C,, la, bridged at the [6,6] bond between C(1) and C(9), and Ib, bridged at the [6,6] bond bctween C(7) and C(8), have been determined. The latter structure is the first one solved for a 7,8-C7, monoadduct. The C,-symmetrical l a and C,-symmetrical l b co-crystallize with CS, molecules in the space groups P2,/c and Pnma, respectively, and the distances between bridgehead atoms are 1.603(3) and 1.584(3) A. The degree of pyramidalization of atoms involved in [6,6] bonds near the 'unsubstituted' pole and near the equator of the fullerene was estimated; it is shown for the unsubstituted pole region that atoms corresponding to C(1) and C(9) are slightly more pyramidal than those corresponding to C(7) and C(8), in agreement with ab initio calculations obtdrned for the C7, spheroid. Some aspects of the crystal packings are discussed.

High‐Temperature Synthesis of the Surprisingly Stable C1‐C70(CF3)10 Isomer with a para7–meta–para Ribbon of Nine C6(CF3)2 Edge‐Sharing Hexagons

“…Distances and angles within the ordered CF 3 groups are normal. The estimated standard deviations (esds) for individual CÀC and CÀF distances in this structure are all 0.003 (except for the CÀF distances in the two disordered CF 3 groups), making this one of the most precisely determined C 70 -containing structures reported to date (the ranges of esds for CÀC bonds within the cage of known structures include 0.002-0.004 for two Diels-Alder monoadducts, [14] 0.004-0.006 and 0.006-0.007 for C 70 (CH 3 ) 8 [13] and C 70 F 38 , [15] respectively, and 0.02-0.03 for C 70 Br 10 , [6] C 70 (IrCl(PPh 3 ) 2 ), [16] and C 70 (Ru 3 (CO) 9 ) [17] ). In addition to further supporting [12] our earlier conclusion [18] that fullerene(CF 3 ) n compounds in general have their CF 3 groups arranged on m-and p-C 6 (CF 3 ) 2 hexagons (most of which form a continuous ribbon through edge sharing) and are not arranged on adjacent (i.e., ortho) cage C atoms as suggested by others, [19][20][21] the structure of C 1 -C 70 (CF 3 ) 10 has revealed several interesting and unanticipated aspects of C 70 X n stereochemistry.…”

Organofullerene Materials

“…These involved cycloaddition of in situ-created reactive ortho-quinodimethane to C 70 and C 76 [109,110], as well as pentamethylcyclopentadiene [111] to C 70 .…”

7,8‐(Dichloromethano)homo[70]fullerene, an Unusual, but Unexceptional, Methanoannulene

“…A search of version 5.24 (November 2002) of the Cambridge Structural Database (hereafter, the CSD) [15] turned up 38 C 70 structures, 22 of which were published during or after 1998, the year of a major review [16]. Only one very precise (uncertainties on CÀC bond lengths in the range 0.001 ± 0.005 ä) C 70 structure [17] has been reported since careful comparisons were made [11] of precise bond lengths determined for three molecules (CSD refcodes LAZMEE [18], ZADQUQ [11], and ZADRAX [11]) and of bond lengths calculated with quantum mechanics. The average bond lengths found for those three molecules change by at most 0.002 ä when a ) The codes for the bond lengths and angles are shown in Fig.…”

“…Definitions of the average bond lengths and angles are shown in Fig. 1; they are the same as have been used previously [11].…”

“…The numbering system follows the IUPAC guidelines issued in 1997 [9] rather than the revised guidelines issued in 2002 [10]; atoms in the second independent molecule are distinguished by primes. The designations of the average distances and angles follow the scheme of Diederich and co-workers [11]. Projections of the two independent molecules as observed at 110, 173, and 295 K are shown in Fig.…”