Single Crystal X-ray Diffraction Study Of Fullerenes And Their Derivatives

Novel carbon allotropes are attracting more and more concerns during recent years. Among them, fullerenes are unique for their solubility and clear molecular structures. The unique spherical structure of fullerenes, full of ?-electrons on the surface, brings numerous fascinating properties. More interestingly, the fullerene interior can host atoms, molecules, and metallic clusters of many types, forming a new family of hybrid materials known as endohedral metallofullerenes(EMFs). The relationship between the internal moieties and the special soccer-ball-like spherical structure makes EMFs very interesting. Besides, their applications in organic solar cell, medicine, etc. has also attracted a lot of research enthusiasm.During the last two decades, people have achieved a lot of research results about the structures and chemical properties of EMFs with many analysis and characterization methods including HPLC, MS, UV-Vis, NMR, TEM, DFT calculation and so on. However, some results obtained previously were turned out to be incorrect by using the single-crystal X-ray diffraction technology and thus the latter method becomes the most reliable way for confirming their structures. In this dissertation, we mainly focus on the synthesis, characterization and especially the crystal structures of a collection of fullerenes, endohedral metallofullerenes and their derivatives. These works and results are summarized as follows:(1) A stable fullerene radical La2@Ih-C80(C7H7) was synthesized by the regioselective reaction of benzyl radical with La2@Ih-C80 and was fully characterized by a collection of experimental and theoretical methods. Although the same Ih-C80 cage is present in Sc3N@Ih-C80 Sc3C2@Ih-C80 and La2@Ih-C80, closed-shell benzylation derivatives were obtained for Sc3N@Ih-C80 and Sc3C2@Ih-C80 whereas an open-shell monoadduct was formed for La2@Ih-C80 . EPR studies and DFT calculations reveal that the La2 cluster can accept the unpaired electron at their ?-bonding orbital to stabilize the open-shell fullerene radical La2@Ih-C80 (C7H7). The short La -La distance, which is comparable to the theoretical value for a La-La single bond, is indicative of metal-metal bonding. Furthermore, electrochemical measurements demonstrate a larger electrochemical gap for 7) than pristine La2@Ih-C80.Our results reveal that the unpaired electron from the exohedral unit can be transferred into the internal metallic cluster through the strong metal-cage interactions.(2) The first isoxazoline derivative of EMFs and a similar derivative of empty fullerene were synthesized via a highly regioselective reaction of 3,5-dichloro-2,4,6-trimethoxy-benzonitrile oxide with Sc3N@Ih-C80 and C6o, respectively. Studies of crystallography and NMR spectroscopy disclose that the isoxazoline ring is fused to a [5,6]-bond junction on Sc3N@Ih-C80 but to a [6,6]-bond junction on C60. A peculiar conformation of the end methoxy group of the substituent in the crystal state of the two adducts were presented, which may provide a valuable clue to the art of conformation control in stereochemistry. In addition, absorption results reveal that the electronic structures of both C60 and Sc3N@Ih-C80 have been altered markedly by the chemical modifications. However, electrochemical results show that the isoxazoline ring has a strong influence on the redox potentials of Sc3N@Ih-C80 but it has no obvious influence on the electrochemical properties of C60.(3) The first organometallic complexes of Sc3N@Ih-C80 and Sc3N@D5h-C80 have been synthesized via a highly regioselective coordination reaction with a tungsten complex W(CO)4(Ph2PC2H4PPh2), representing as the first examples of air-stable mononuclear coordination compounds of EMFs. X-ray crystallographic results reveal that the tungsten center attaches to a specific [6,6]-bond of each Sc3N@C80 isomer in an ?2 fashion, affording the first derivatives with a closed three membered ring of Sc3N@C80. Interestingly, although Vis-NIR and IR results demonstrate negligible exohedral metal to ligand charge transfer, i.e. relatively weak ? back-donation from the metal center to the fullerene ligand in both complexes, the two complexes show remarkable air-stability which may enlighten their potential applications in such field as biology, electronics, catalysis and optics.(4) A series of single crystals of fullerenes, endohedral fullerenes and their derivatives were characterizated by X-ray diffraction crystallography, and their definite structures were obtained. Crystallographic results disclosed some new findings as follows. a). a sandwich-like structure was obtained when co-crystalize 2,7-dibenzylbenzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone with C6o in benzene, which could further enhance the ?-? interaction between C60 and benzene. b). the pentane-fused structure of the adduct generated by the reaction between C60 and triethylamine was confirmed. c). the crystallographic studies of serveral derivatives generated by reacting 1,2-bis(azidomethyl)-benzene with C60 or C70 were carried out, which further helps verifying the mechanism of the tether reaction, d). the crystal structure of the first Pr-based EMFs (Pr@C2v-C82) was inverstigated, suggesting strong interaction between internal Pr atom and the fullerene carbon cage. e). the structure of the first pyrazole-ring fused derivative of EMFs was obtained. f). the structure of the first derivative of EMFs generated by the Lewis acid-base complexation reactions with NHCs was elucidated, suggesting the unprecedented addition sites at the abnormal carbene carbon atom on the exohedral group and the relatively inert [6,6,6]-carbon atom on the fullerene cage.