Soluble Chlorofullerenes C60Cl2,4,6,8,10. Synthesis, Purification, Compositional Analysis, Stability, and Experimental/Theoretical Structure Elucidation, Including the X-ray Structure of C1-C60Cl10
journal contributionposted on 12.05.2010, 00:00 by Igor V. Kuvychko, Alexey V. Streletskii, Natalia B. Shustova, Konrad Seppelt, Thomas Drewello, Alexey A. Popov, Steven H. Strauss, Olga V. Boltalina
The efficacy of various analytical techniques for the characterization of products of C60 chlorination reactions were evaluated by (i) using samples of C60Cl6 of known purity and (ii) repeating a number of literature syntheses reported to yield pure C60Cln 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 C60Cln 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 C60 by ICl, ICl3, and Cl2 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-C60Cl2, 1,9-C60Cl2, 1,6,9,18-C60Cl4, and 1,2,7,10,14,24,25,28,29,31-C60Cl10. The latter compound was also studied by 13C NMR spectroscopy and X-ray diffraction, which led to the unambiguous determination of its asymmetric addition pattern. The unusual structure of C60Cl10 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 C60Cl10 from C60Cl6 and excess ICl without the rearrangement of any C−Cl bonds. For the first time, the stability of C60Cln 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 C60Cl6 was also redetermined with higher precision.