Study On Soluble Lanthanum-containing Endohedral Metallofullerenes

Fullerene is the only zero-dimensional crystalline form of carbon allotrope with accurate molecular structures,and its interior can encase metal atoms or metal clusters to form a new kind of hybrid materials,endohedral metallofullerenes(EMFs).EMFs bear the properties of both the encaged metals and the carbon cage due to the charge transfer from the encaged metals to the carbon cage.EMFs are particularly attractive because of their unique structures and vast potential applications in medicine,materials science and electronics.The study in this dissertation concentrates on the synthesis,extraction,separation,characterization and chemical modification of a series of soluble lanthanum-containing EMFs.The results and conclusions in this work are as follows:1.A wide array of soluble lanthanum-containing EMFs LaC2n(2n = 84,86,88,94,96)and La2C2n(2n = 92,94,96,98,100,102,104 and 106)have been successfully obtained,namely,three isomers of La@C84,one isomer of La@C86,two isomers of La@C88,three isomers of La@C94,three isomers of La@C96,two isomers of La2@C92,three isomers of La2@C94,three isomers of La2@C96,three isomers of La2@C98,four isomers of La2@C100,four isomers of La2@C102,four isomers of La2@C104 and three isomers La2@C106.The purity,cage symmetry and chemical stability of these isomers were characterized by laser desorption/ionization time of flight mass spectrometry(LDI-TOF-MS),high performance liquid chromatography and Vis-NIR spectroscopy.Based on different absorption features,La2C94(Ⅰ),La2C102(Ⅲ),La2C106(Ⅰ)and La2C106(Ⅱ)are supposed to be higher carbide cluster metallofullerenes(CCMFs)La2C2@D3(85)-C92,La2C2@D5(450)-C100,La2C2@Cs(574)-C102,La2C2@D3d(822)-C104 and La2C2@C2(816)-C104,respectively.In addition,La2C100(Ⅲ)are supposed to be higher dimetallofullerene La2@D5(450)-C100.2.The six most abundant isomers,La2C2n(2n = 92,94,96,98,100),have been structurally characterized as higher CCMFs La2C2@C2(41)-C90,La2C2@D3(85)-C92,La2C2@C2(69)-C92,La2C2@C1(132)-C94,La2C2@C2(157)-C96 and La2C2@C1(175)-C98 by single-crystal X-ray diffraction.It is evident that the cage length increases roughly along with increase of the carbon atom number,resulting in an increase of the La-La distance and the Ni…cage distance as well.It is suggested that the shape、size and cage symmetry of the carbon cages have a remarkable influence on the interactions between the endohedrals and the NiⅡ(OEP)molecules,finally determining the arrangement in the crystal state.Our experimental and theoretical results have unambiguously confirmed that La2C2n(2n = 92-100)tend to form CCMFs La2C2@C2n(2n = 90-98)instead of di-EMFs La2@C2n(2n = 92-100).Two main reasons should account for the preferential formation of CCMFs.Electronically,the C2-unit can accept a partial amount of charges from the metal atoms and thus the charge density on the cage surface is reduced.Geometrically,the C2-unit can link the two La ions to fulfill their coordination requirement as much as possible,thus stabilizing the whole molecules.3.The photochemical reaction of La2C2@D3(85)-C92 with 2-admantane-2,3-[3H]-diazirine and the 1,3-dipolar reaction of La2@D5(450)-C100 with 3-triphenylmethyl-5-oxazolidinone are studied for the first time,respectively.It is found that the bandgap of La2C2@D3(85)-C92Ad(0.93 eV)is larger than that of La2C2@D3(85)-C92(0.83 eV),indicating better chemical stability of the former one.During the reaction of La2@D5(450)-C100 with 3-triphenylmethyl-5-oxazolidinone,the intensities of the two monoadducts increase with the extended heating time,and the relative intensities of these two monoadducts are nearly identical.