Synthesis,structural Characterization And Functionalization Of Lutetium-containing Metallofullerenes

As the only zero-dimensional crystalline form of carbon allotrope with accurate molecular structures,fullerenes can encapsulate a variety of metal atoms or metallic clusters,forming a new class of novel hybrid molecules,defined as endohedral metallofullerenes?EMFs?.EMFs possess many new properties because of the charge transfer from the internal metals to the outer cage.Exploring the novel EMFs and studying their physical and chemical properties are very important for the understanding of the correlation between structure and property,the formation mechanism of EMFs,and the development of new carbon nanomaterials with potential applications.In this dissertation,we mainly focus on the preparation,purification,characterization and chemical functionalization of a collection of lutetium-containing EMFs.These works and results are summarized as follows:?1?Using Lu₂O₃ as the metal source,we synthesized a series of Lu-containing EMFs with various cage sizes and symmetries,Lu₂@C_2n?2n = 76-88?,by the arc-discharge method,which were isolated by high performance liquid chromatography?HPLC?.Crystallographic results of these new compounds show that they are Lu₂@Td?2?-C₇₆,Lu₂@D3h?5?-C₇₈,Lu₂@C₂v?5?-C₈₀,Lu₂@Cs?6?-C82,Lu₂@C3v?8?-C₈₂,Lu₂@C₂v?7?-C₈₄,Lu₂@D₂d?23?-C₈₄,Lu₂@Cs?8?-C₈₆,Lu₂@C₂v?9?-C86,Lu₂@Cs?15?-C86) and Lu₂@C1?26?-C₈₈,respectively.Interestingly,it is revealed that the Lu-Lu distances between the two Lu ions of all Lu₂@C_2n?2n = 76-88?isomers fall in the range of a Lu-Lu single bond length?3.28-3.81 ??observed from the literatures.Thus,we have confirmed experimentally that a Lu-Lu single bond is formed between the two mutually exclusive Lu ions.Moreover,theoretical results show that each Lu atom formally donates a 5d electron and a 6s electron to the cage with the remaining 6s electron shared with the other Lu atom to form a Lu-Lu single bond,so that only four electrons are transferred to the fullerene cages with the formal divalent valence for each lutetium ion.In addition,the electrochemical study reveals that Lu₂@C_2n?2n = 76-88?isomers all possess relatively large electrochemical gaps,suggesting their high stability,and it appears that the reversibility of the redox processes is improved when the cage becomes larger.?2?Seven Lu-containing carbide EMFs,Lu₂C₂@C_2n?2n = 86-92?,were synthesized and isolated,and their purity,cage symmetry,electronic structure and molecular stability were characterized by laser desorption/ionization time of flight mass spectrometry?LDI-TOF-MS?,HPLC and Vis-NIR spectroscopy.The electrochemical study show that Lu₂C₂@C_2n?2n = 86-92?isomers all possess closed-shell electronic structures.Single-crystal XRD crystallographic results unambiguously assigned the molecular structures of these compounds as Lu₂C₂@C₂v?9?-C86,Lu₂C₂@Cs?32?-C₈₈,Lu₂C₂@D2?35?-C₈₈,Lu₂C₂@Cs?hept?-C₈₈,Lu₂C₂@C₂?41?-C90,Lu₂C₂@C₂?43?-C90 and Lu₂C₂@D3?85?-C92,respectively.Moreover,crystallographic results reveal that the Lu-Lu distances between the two Lu ions of all Lu₂C₂@C_2n?2n = 86-92?isomers are longer than the length of a Lu-Lu single bond,thus the Lu-Lu bonding is broken and a C₂ unit is requested to fulfill the coordination requirement of the Lu ions and stabilize the corresponding molecules,resulting in the formation of carbide EMFs,Lu₂C₂@C_2n?2n = 86-92?.After the comprehensive comparison of the crystallographic results of Lu₂@C_2n?2n = 76-88?isomers,we have confired that not only the exact configuration of the internal metallic cluster,but also the shape of Lu₂C₂ cluster are all determined by the cage size.?3?Using Lu₂O₃ and N₂ as the respective metal and nitrogen sources,we synthesized a series of Lu-containing trimetallic nitride EMFs with various cage sizes and symmetries,Lu₃N@C_2n?2n = 80-88?,by the arc-discharge method,which were isolated by HPLC.Their structures are unambiguously determined as Lu₃N@Ih?7?-C₈₀,Lu₃N@D5h?6?-C₈₀,Lu₃N@C₂v?9?-C82,Lu₃N@Cs?51365?-C₈₄,Lu₃N@D3?17?-C86 and Lu₃N@D2?35?-C₈₈ by single-crystal XRD crystallography.Furthermore,our results reveal for the first time that the Lu₃ N cluster keeps its planar geometry in all the C₈₀-88 cages to ensure sufficient metal-cage/metal nitrogen interactions.The electrochemical study reveal that Lu₃N@C_2n?2n = 80-88?isomers all possess relatively large electrochemical gaps,suggesting their high stability,and it is confirmed that changing the cluster species and the cage symmetry significantly affect the redox properties of EMFs.?4?We have systematically investigated the Lewis acid-base pairing reaction between strained N-heterocyclic carbene?NHC?and four different lutetium-containing EMFs(Sc3N@Ih?7?-C₈₀,Lu₃N@Ih?7?-C₈₀,Lu₂@C3v?8?-C82 and Lu₂@C₂v?9?-C82).Interestingly,our experimental results show that a C-C single bond is formed between the NHC group and a specific cage carbon of the corresponding EMF.Moreover,changing the variables that affect the reactions,such as the reaction atmosphere,the configuration of the internal metallic cluster,the carbon cage size and the steric hindrance of the NHC moiety,only one mono-adduct with specific addition pattern and molecular structure is obtained for each EMF,demonstrating surprisingly high reactivity and regioselectivity.In addition,the purity,electronic structure and molecular structure of these mono-adducts were characterized by LDI-TOF-MS,Vis-NIR spectroscopy and single-crystal XRD crystallography.After the comprehensive comparison of our crystallographic and computational results,we have confirmed that the remarkably high regioselectivity and the quantitative formation of mono-adducts of the Lewis acid-base pairing reaction between NHC and EMFs are direct results from the distributions of molecular orbital and electrostatic potential on the cage surfaces,in addition to the previously assumed steric hindrance between the fullerene cage and the NHC moiety.