Chemical Properties Of Higher Endohedral Fullerenes And Empty Fullerenes

As the only carbon allotrope with definit molecular structure,fullerenes have been attracted widespread attention due to their perfect spherical structures and excellent properties.During the formation process of fullerenes,atoms,ions and clusters are facily trapped into their cavities to form different types of endohedral metallofullerenes.The carbon cage surface of fullerenes comprised of large?-conjugated electron system enable them versatile chemical properties.The chemical properties of endohedral fullerenes are different from conventional fullerenes such as C60 or C70 due to the eletron transfer from the entrapped clusters to carbon cages.In addition,the chemical properties of higher empty fullerenes have been rarely explored owing to their larger number of ? electrons and lower structural symmetry relative to that of C60/C70.In order to achieve the in-depth understanding of chemical properties of endoedral fullerenes and higher empty fullerenes,the trifluoromethylation and chlorination reaction were employed to achive corresponding fullerene derivatives.Importantly,all the molecular structures of fullerene derivatives are unambiguously confirmed by single crystal X-ray diffraction.The addition site distribution of addends atttacted onto carbon cages and the influence of exohedral addends on the geometric configurations change of entrapped clusters in the carbon cage are discussed,facilitating the further understand of corresponding reaction mechanism.The relevant research contents are mainly divided into the following four aspects:(1)Y2C2@Cs(6)-C82 was chemically modified-with the reaction of iodotrifluoromethane under high temperature conditions,affording four isomers of endohedral fullerene derivatives bearing 16 addition addends as Y2C2@C82(6)(CF3)16.The addition positions of 16 trifluoromethyl groups on the surface of carbon cages and the spatial configuration of yttrium carbides clusters inside the carbon cage were unambiguously determinded by single-crystal X-ray diffraction.The encapsulated Y2C2 cluster within the Cs-Cs2(6)carbon cage exhibits a butterfly-shaped geometry.More interestingly,the relative positions of the two cage pentagons on the carbon cage depend on the addition pattern of 16 trifluoromethylation,resulting in a significant change of the butterfly geometry of Y2C2 cluster,where the Y…Y distance alters from 3.544 to 4.051A.Through the trifluoromethylation reaciton,the geometry of Y2C2 cluster within the same carbon cage can be readily steered via different spatial distribution of the addends,offering a new opportunity to tailor the structure and property of endohedral fullerene toward versatile applications.(2)YCN@C82 and YCN@C84 were used as raw materials to react with iodotrifluoromethane under high temperature,showing that the effect of different carbon cages with embedded cyanide clusters on trifluoromethylation was studied.A series of derivatives of YCN@Cs(6)-C82 with an addends number ranging from 12 to 20 were obtained,and corresponding molecular structures of YCN@C82(6)(CF3)16/18 were determinded by single crystal X-ray diffraction,comfirming that the trifluoromethyl groups were attacted to the 11 pentagons on carbon cage and the remaining pentagons was used to coordinate with yittrium.Subsequently,we studied the chemical properties of cyanide clusterfullerenes with higher carbon cage,YCN@C84(23)and YCN@C84(13)by the reaction with iodotrifluoromethane at a high temperature,affording YCN@C84(CF3)16/18.The crystallographic results clearly showed the molecular structure of YCN@C84(23)(CF3)18 and three YCN@C84(13)(CF3)16 isomers.Through the analysis of these single crystal structures,we found that the CF3 group were free from pentagons interacting with the Y atom,and the CF3 group was attacted to the position where the three hexagons connected,which are different from empty fullerenes and similar to the case of YCN@C82(6).More importantly,the triangle geometry of the embedded cluster YCN depend on the addition sites of the CF3 group in the structure of YCN@C8a(CF3)16/18,which indicates that CF3 groups have a significant influence on the geometry of the embedded cluster YCN.In addition,the addition sites distribution of CF3 groups is also related to the carbon cage symmetry of YCN@C84 by comparing the YCN@C84(23)(CF3),8 and three isomers of YCN@C84(13)(CF3),6.YCN@C82(6)(CF3)16/18 and YCN@C84(CF3)16/18 featuring CF3 addition patterns are stabilized by the formation of isolated C=C bonds and benzenoid ring on the carbon cages.By the trifluoromethylation reaction of cyanide clusterfullerenes,we clarified the relationship between the geometry configuration of the embedded cluster YCN and the addition site distribution of the exohedral CF3 groups.(3)Higher empty fullerenes have completely different chemical reaction compared to that of convential C60/C70 due to the increased ?-electron system and lower structural symmetry.In order to explore the chemical properties of higher fullerenes,the fullerene mixture containing C88 and C92 were modified via high-temperature chlorination.The unexpected product as C84Cl30 was obtained and was confirmed by single crystal X-ray diffraction,showing that the structure of C84Cl30 contains two heptagons,two pairs of quaternary sequentially fused pentagons and two pairs of fused pentagons.By combinated with the carbon cage skeleton transformation mechanism,we propose that the formation of C84Cl30 is attributed to two C2 losses and two Stone-Wales rearrangements from the unreported C2-C88(3),consquently resulting in the skeleton shrinkage from C88 to C84 carbon cage.(4)In order to explore the chemical properties of higher empty fullerenes,we performed the high temperature chlorination reaction,acheving a series of fullerene derivatives as C98(107,109)Cl20/22,C98(120)Cl18/22 and Cs-C104(234)Cl16/18,D2-C104(812)Cl12/24,C2-C104(811)Cl28 and C1-C104(258)Cl16.The molecular structures of fullerene derivatives mentioned above were ambiguously confirmed by single crystal X-ray diffraction,showing that three new isomers of C98 fullerenes labled as 107,109 and 120 were found in the chlorinated derivatives of C98.At the same time,The crystal structures for C104(234)Cl16/18,C104(812)C112/24,and C104(811)C128 revealed that along with the successive additions of Cl atoms onto fullerene cages proceed,retaining the substructures of the less chlorinated derivatives are still kept during the chlorinated process of three isomers of C104.In addition,the addition positions distribution of chlorine atoms were mainly located at both ends of higher fullerenes due to that 12 pentagons separated by hexagons located at the similar positions,which were confirmed by the single crystal X-ray diffraction.This section contributes to the understood of chemical properties of higher fullerenes.