Synthesis, Isolation, Structures And Properties Of Novel Terbium-based Endohedral Fullerenes

Endohedral fullerenes represent a special type of fullerenes with atoms, ions, or clusters trapped in their inner space. Exploring novel endohedral fullerenes is important for the understanding of the correlation between structure and property, the formation mechanism of endohedral fullerenes, and the development of new functional materials for the potential applications, thus it has been an important topic of fullerene research. In this dissertation, we focus on the synthesis, isolation, structures and properties of novel terbium (Tb)-based endohedral fullerenes, and have carried out the following works:1) A pure isomer of Tb2C84was successfully synthesized and isolated, and its molecular structure was determined by single crystal X-ray diffraction study to be Tb2C2@Cs(6)-C82. X-ray diffraction study reveals that a bent Tb2C2carbide cluster is encaged rigidly inside a Cs(6)-C82cage, and the encaged Tb atoms locate with one Tb atom being beneath a hexagon and another Tb atom pointing to the conjunction of two adjacent hexagons. The C-C bond within the encaged Tb2C2carbide cluster behaves as a typical C-C triple bond. Compared with those of the reported analogous M2C2@Cs6)-C82(M=Sc, Tm), Tb2C2cluster of Tb2C2@Cs(6)-C82was constrained more rigidly by the cage and became more bent than Sc2C2clusterbent. The UV-vis-NIR spectrum of Tb2C2@Cs(6)-C82highly resembles to those of M2C2@Cs(6)-C82(M=Sc, Tm, Tb). However, the redox behavior of Tb2C2@Cs(6)-C82differed obviously from that of Sc2C2@Cs(6)-C82, and this is probably caused by the contribution of the encapsulated Sc atoms to the frontier molecular orbital of Sc2C2@Cs(6)-C82.2) Several novel Tb-based metal cyanide clusterfullerenes (CyCFs), including TbNC@C2v(19138)-C76as the first non-IPR CyCF and three isomers of TbNC@C82(C2(5), Cs(6), C2v(9)), have been successfully synthesized, isolated and characterized by single crystal X-ray diffraction study. We find that the entrapped TbNC cluster is unusually flexible, which changes the geometric structure and the Tb-N(C)/C-N bond lengths dramatically upon varying the isomeric structure or size of the fullerene cage. When the isomeric structure of C82cage varies from C2(5), Cs(6) to C2v(9), the triangular TbNC cluster within TbNC@C82exhibits obvious distortions with the Tb-C(N)-N(C) angle varying by up to20and the C-N bond length increases gradually from0.94(5),1.03(3) to1.07(5) A. When the cage size decreases from C82to C76, the TbNC cluster experiences a severe distortion from the triangular geometry to a nearly linear structure, and the C-N bond length elongates further to1.096(19) A. In specific, the significant distortion from the triangular geometry to a nearly linear structure of the entrapped TbNC cluster upon decreasing the cage size from C82to C76is interpreted by the weakening of the coordination bonding between Tb and CN-ligand and consequently a stronger Tb-cage interaction which contributes to the stabilization of the fused pentagons of TbNC@C2v(19138)-C76. The geometric structure changes of the entrapped TbNC cluster within TbNC@C82(C2(5), Cs(6), C2v(9)) directly lead to the change of their electronic properties in terms of the decrease of both optical and electrochemical band-gaps from C2(5), Cs(6) to G2v(9) isomers. The TbNC cluster represents the first flexible cluster found for endohedral fullerenes, and our discovery of the flexibility of endohedral cluster opens up a new avenue to modulate the properties of endohedral fullerenes via shaping the geometric structure of the entrapped species.3) A novel Tb/Ti mixed metal μ3-carbido clusterfullerene, TiTb2C@Ih(7)-C80, was successfully synthesized and isolated. The UV-vis-NIR spectrum of TiTb2C@Ih(7)-C8o shows a high resemblance to that of the recently reported TiLu2C@Ih(7)-C80, suggesting their similar molecular and electronic structures of [(Tb3+)2(Ti3+=C3-)]6+@[Ih(7)-C80]6-. Furthermore, the electrochemical study reveals that, upon substituting the encaged Lu by Tb atom, the redox property of TiLu2C@Ih,(7)-C80did not change obviously, suggesting thatthe electrochemical property of TiLn2C@Ih(7)-C8o (Ln=Tb, Lu) is independent on the encapsulated lanthanide metal Ln.4)12nitrogen-containing inorganic solid compounds with variable oxidation states of nitrogen and counter ions, including ammonium salts ((NH4)XH3-xPO4(x=0-2),(NH4)2SO4,(NH4)2CO3, NH4X (X=F, Cl), NH4SCN), thiocyanate (KSCN), nitrates (Cu(NO3)2, NaNO3) and nitrite (NaNO2), were successfully applied as new inorganic solid nitrogen sources toward the synthesis of Sc-metal nitride clusterfullerenes (NCFs). Among them, triammonium phosphate hydrate ((NH4)3PO4·3H2O) and ammonium thiocyanate (NH4SCN) are revealed to behave as better nitrogen sources than others, and the highest yield of Sc-NCFs was achieved when NH4SCN was used as a nitrogen source. The optimum molar ratio of Sc2O3:(NH4)3PO3·3H2O:C and Sc2O3:NH4SCN:C has been determined to be1:2:15and1:3:15, respectively. An "in-situ" preheating treatment by contacting two electrodes under a very low DC current has been also developed as another strategy to optimize the synthesis conditions in order to remove the hydrated/adsorbed water of these inorganic compounds. The new synthesis method by using a series of inorganic solid nitrogen sources is expected to be developed as a general route to the high yield synthesis of NCFs, and the versatility of the nitrogen sources revealed in this study provides a new insight into the chemical reactions involving NCF formation during arc-discharging.5) By introducing sodium nitrate (NaNO3) as an additive for the synthesis of the Sc-containing endohedral fullerenes, Sc3N@C79N was successfully synthesized, while its isolation and structural characterization were not fulfilled yet presumably due to its low stability and easy ionization during mass spectroscopic measurement. In addition, a new fullerene compound the molecular weight of720(named as Fullerene-720) was successfully synthesized and isolated. UV-vis-NIR spectrum of Fullerene-720is dramatically different to that of the well-knownn,Ih-C60Electrochemical characterizartion of Fullerene-720indicates that its redox processes are irreversible.