Synthesis,Separation,Crystallographic Structures And Chemical Properties Of Yttrium-containing Metallofullerenes

Fullerenes are a new type of carbon materials with accurate molecular structures,the investigation of fullerenes is significant for in-depth acquaintance of the carbon materials.The internal space of fullerenes can host metal atoms and clusters,forming a new family of hybrid materials known as endohedral metallofullerenes(EMFs),and the interaction between encapsulated species and cage in EMFs makes them possess more special properties.The structural elucidation of EMFs is the most important and fundamental work,which is the basis for researching their chemical properties and applications.However,the structural elucidation of EMFs is more difficult than that of empty fullerenes because of the interal metal atoms,and many incorrect structures of EMFs were reported previously because of the lack of unambiguous experimental results,which now are able to achieved by the powerful single-crystal X-ray diffraction crystallography.The reported studies including crystal structures of EMFs are mainly limited to scandium-and lanthanum-based metallofullerenes to now.In comparison,the EMFs containing medium-size metal such as yittrium is sufficiently rare to be studied.Herein we focus on the synthesis,separation and characterization of a series of yttrium-based mono-metallofullerenes(mono-EMFs),di-metallofullerenes(di-EMFs)and carbide cluster metallofullerenes(CCMFs),and investigate their crystallographic structures and chemical properties.These results are summarized as follows:(1)The soot containing yttrium-based EMFs was prepared through direct current arc discharge method and extracted with N,N-dimethylformamide(DMF)or carbon disulfide(CS2).The analysis of the crude extraction shows that the polar solvent DMF is efficient to selectively extract Y@C82 isomers while CS2 is able to extract giant metallofullerenes Y2C92-150.Then forteen yttrium-based EMFs are obtained,namely,Y@C76,two Y@C82 isomers,two Y2@C82 isomers,Y2C84,Y2C88,two Y2C90 isomers,two Y2C92 isomers and three Y2C94 isomers.The purity and cage symmetry of these compounds were characterized by high performance liquid chromatography(HPLC),laser desorption/ionization time of flight mass spectrometry(LDI-TOF-MS)and Vis-NIR spectroscopy,and the results show Y@C82-?,Y2C82-?,Y2C82-?,Y2C84-?,Y2C90-?,Y2C92 and Y2C94-? should possess the C2v(9)-C82,Cs(6)-C82,C3v(8)-C82,Cs(6)-C82,D2(35)-C88,C2(41)-C90 and D3(85)-C92 cages,respectively.The electrochemical properties of Y@C82-??Y2C82-??Y2C82-??Y2C92-? and Y2C94-? were characterized by cyclic voltammetry.Besides,the treatment with SnCl4 applied to separation is rather effective to completely separate Y-based EMFs from empty fullerene,which facilitates the subsequent HPLC separation.(2)The single crystals of isolated Y-based EMFs were obtained through the cocrystallization with Ni(octaethylprophyrin)(OEP),and further X-ray diffraction studies unambiguously identified their molecular structures,namely,Y@Td(2)-C76,Y@C2v(9)-C82,Y@Cs(6)-C82,Y2@Cs(6)-C82,Y2@C3v(8)-C82,Y-C2@Cs(6)-C82,Y2C2@Cs(15)-C86,Y2C2@C1(26)-C88,Y2C2@C2(41)-C90,Y2C2@C2(43)-C90 and Y2C2@C2(61)-C92.Note worthily,a regioselective dimerization is observed in the crystal state for Y@Cs(6)-C82,caused by the localization of high spin density on a special carbon atom of Y@Cs(6)-C82.The crystallographic results of Y2C2n(2n=82,84,88-94)show the Y-Y distance elongates along with the increase of cage size and the two yittrium atoms are linked by a direct metal-metal bond in Y2@CS(6)-C82 and Y2@C3v(8)-C82.In addition,the observed disordered resluts of the internal metal atoms for Y2C2n(2n=82,84,88-94)show the C2 unit and the cage size have an significant influence on the motion of internal metal atoms.(3)The chemical properties of Y@C2v(9)-C82 and Y2@C3v(8)-C82 were studied through the photoreaction of Y@C2v(9)-C82 with Re2(CO)10,the reaction of Y@C2v(9)-C82 with N-arylbenzamidine catalyzed by Ag2CO3,three 1,3-dipolar reactions of Y2@C3v(8)-C82 with diphenylnitrilimin,N-triphenylmethyl-5-oxazolidinone and N-methoxymethyl-N-(trimethylsilyl)-benzylamine,and a series of derivatives including a rhenium complex(la)and a imidazoline derivative of Y@C2,(9)-C82(3a)as well as a pyrazol derivative(5a)and three pyrrolidino derivatives of Y2@C3v(8)-C82(4a,4b and 6a)were successfully synthesized,separated and characterized.Vis-NIR spectra of 4b,5a and 6a reveal they should possess similar electronic structures.The electrochemical properties and crystallographic structures of la,5a and 6a were measured through cyclic voltammetry and single-crystal X-ray diffraction respectively.The crystallographic results of la show the rhenium atom coordinates with[5,6,6]carbon atom,forming a unique complex Re(CO)5(?-Y@C2v(9)-C82),noteworthily,this is the first report of ?1-metallofullerene metal complex.The crystallographic results of 5a and 6a reveal that the 1,3-dipolar additions occur on a[6,6]junction of the sumanene-type hexagon and the internal Y-Y bond forms inside carbon cages,which is similar to the situation of pristine Y2@C3v(8)-C82.