Soluble chlorofullerenes C(60)Cl(2,4,6,8,10). Synthesis, purification, compositional analysis, stability, and experimental/theoretical structure elucidation, including the X-ray structure of C(1)-C(60)Cl(10).
The efficacy of various analytical techniques for the characterization of products of C(60) chlorination reactions were evaluated by (i) using samples of C(60)Cl(6) of known purity and (ii) repeating a number of literature syntheses reported to yield pure C(60)Cl(n) compounds. The techniques were NMR, UV-vis, IR, and Raman spectroscopy, FAB, MALDI, LDI, ESI, and APCI mass spectrometry, HPLC, TGA, elemental analysis, and single-crystal X-ray diffraction. Most of these techniques are shown to give ambiguous or erroneous results, calling into question the composition and/or purity of nearly all C(60)Cl(n) compounds reported to date. The optimum analytical method for chlorofullerenes was found to be a combination of HPLC and either MALDI or APCI mass spectrometry. For the first time, the chlorination of C(60) by ICl, ICl(3), and Cl(2) was studied in detail using dynamic HPLC analysis and APCI mass spectrometry. Suitable conditions were found for the preparation of the new chlorofullerenes 1,7-C(60)Cl(2), 1,9-C(60)Cl(2), 1,6,9,18-C(60)Cl(4), and 1,2,7,10,14,24,25,28,29,31-C(60)Cl(10). The latter compound was also studied by (13)C NMR spectroscopy and X-ray diffraction, which led to the unambiguous determination of its asymmetric addition pattern. The unusual structure of C(60)Cl(10) was compared with other possible isomers using DFT-predicted relative energies. These results, along with additional experimental data and an analysis of the DFT-predicted frontier orbitals of likely intermediates, were used to rationalize the formation of the new compound C(60)Cl(10) from C(60)Cl(6) and excess ICl without the rearrangement of any C-Cl bonds. For the first time, the stability of C(60)Cl(n) compounds under a variety of conditions was studied in detail, leading to the discovery that they are, in general, very light-sensitive in solution. The X-ray structure of C(60)Cl(6) was also redetermined with higher precision.