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Endohedral metallofullerenes have special structures, therefore we are interested in. High-temperature laser vaporization method and direct current arc discharge method, which are the two methods for preparing endohedral metallofullerenes. Here we study the preparation of endohedral metallofullerenes by direct current arc discharge method, which uses two graphite rods as electrode and vaporizes the one which infill metal complex in high temperature and low helium gas pressure environment. We study in some metal complexes such as Mo(C5Ph5)2, Fe(CO)9, Ag and Au. After reaction, we collect the soot produced in reaction and choose different solvents to separate the products from it with Soxhlet extraction.

The chemistry of fullerenes, which are a class of carbon allotropes that can be prepared by vaporization of graphite in an electric arc in a low pressure atmosphere,1 has become a topic of much experimental and theoretical study over the past 25 years.  Herein we present a series of theoretical studies related to recently discovered or studied endohedral metallofullerenes (EMF) and a theory as to the selective stability of certain isomers of EMFs. Computational treatments of the anions of C80 and C94 are presented and compared in an effort to gain an understanding and predictive model for which isomers of each cage size EMF will be most stable.  A model is proposed in which the pentagons of fullerene anions are seen as charge localization centers that repel one another, making the pyracyclene bonding motif much more unstable for fullerene anions than for fullerene neutral cages. Computational treatments are also presented for two newly discovered EMFs, Y2C2@C92 and Gd2@C79N.  Y2C2@C92 is reported to exhibit a previously undiscovered mode of internal cluster rotation, while Gd2@C79N is shown to have unusual stability for an azofullerene with a large spin quantum number (15/2). Finally, computational techniques are employed to predict the thermodynamic feasibility of a chemical reaction replacing one metal atom in a trimetallic-nitride template (TNT) endohedral metallofullerene with different metal atom.  At least two of these are predicted to be thermodynamically practical. / Ph. D.

Two distinct research projects were carried out in this dissertation. In the first project the results of first principle calculations on endo- and exohedral complexes of polyhedral oligomeric silsesqiuoxanes (POSS) with atomic and ionic species were carried out. Detailed studies were performed on structures, stabilities and electronic properties of these complexes. The stabilities of the endohedral Tn-POSS ( n = 8, 10 and 12) complexes depends on both the cage size and the nature of the endohedral species. Alkali metal ion encapsulation leads to cage contraction. Electron density was transferred from the cage to the alkali metal cations. Halide encapsulation caused the cages to expand. Electron density was transferred from the halides to the cage. Noble gas encapsulation has minimum effect on the cage structure. Electron transfer between cage framework atoms and He and Ne were negligible. However, a small amount of electron transfer between Ar and POSS cages occurred. Ionization potentials calculated for T10-POSS and T12-POSS endohedral complexes with alkali metals indicate that these complexes have "superalkali" behavior. Several transition metal encapsulations into the T8-POSS cage gave thermodynamically stable endohedral complexes. The HOMO-LUMO gaps for the transition metal endohedral complexes were reduced versus that of pure cage. In almost all cases, the exohedral Tn (n = 8, 10, 12) complexes were energetically more stable than their corresponding endohedral counterparts except for the complex with F-. The exohedral Fpenetrates directly into the Tn-POSS cage forming an endohedral complex. In the second project ab initio electronic structure calculations based on density functional theory were performed to study small silicon clusters containing an endohedral atoms or ions. The formation of endohedral clusters M@Si12 (Li0,1,-1, Na0,1,-1, K+, He, F- and Cl-) depended on the Si12 cage structure and the nature of the embedding species. Only Li0,1,-1, Na0,1,-1 and He form endohedral clusters with different Si12 cage isomers. All observed endohedral clusters are stable and have large HUMO-LUMO gaps (>1eV). The endohedral clusters Li-@Si12 and Na-@Si12 are thermodynamically more stable than their neutral and cationic counterparts. The stability order predicted for the alkali metal series was anionic clusters > neutral clusters> cationic clusters. Encapsulations of halides are completely unfavorable and halide insertions cause the Si12 cage rupture. Encapsulation of two Li atoms into the Si18 cage generates the endohedral Li2@Si18 complex. Encapsulating Na atoms into Si18 cage leads to an exohedral Na2Si18 cluster. Endohedral Si20@Li20 was also investigated and characterized.

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En este trabajo abarcamos el estudio de la estructura electrónica de una serie de fulerenos denominados fulerenos endoédricos, así como también su reactividad. En este trabajo de tesis previo, se define lo que se conoce como la regla del gap (LUMO-3)-(LUMO-4), la cual indica que aquellas cajas fulerénicas vacías cuyo gap entre el tercer y cuarto orbitales desocupados sea mayor grande tendrán la capacidad de aceptar la transferencia de seis electrones desde un clúster metálico. En el capítulo 3, la regla del gap (LUMO-3)-(LUMO-4) ha sido extendida para aquellas cajas fulerénicas de hasta 100 átomos de carbono. También se ha analizado la reactividad exoédrica del M3N@D5h-C80 en una reacción de cicloadición de Diels-Alder con 1, 3-butadieno sobre los diferentes tipos de enlaces de la caja D5h-C80. En el capítulo 4 estudiamos la estructura electrónica de los fulerenos endoédricos con carburos metálicos (M2C2@C82). Se han estudiado seis isómeros de Sc2C2@C82, confirmando que su estructura electrónica se puede explicar de manera sencilla con el modelo iónico (clúster)4+@(caja)4–, adoptando el carburo metalico diferentes orientaciones dentro de la caja de C82 . En el capítulo 5 hemos estudiado la estructura y propiedades electrónicas de una otras dos famílias de fulerenos endoédricos: la de los óxideos de escandio y la de los sulfuros de escandio. Por último hemos estudiado las propiedades electroquímicas de una serie de fulerenos endoédricos con diferentes clústeres (capítulo 6). Los orbitales frontera y las propiedades redox de Sc3N@C80 son diferentes cuando son comparados con fulerenos endoédricos de metales más electro positivos (Gd e Y). / We have extended the application of the general rule for the stabilization of nitride EMFs proposed by Campanera et al. to IPR carbon cages of dimensions up to C100. This simple rule, based on the formal transfer of six electrons from the cluster to the carbon cage, can be seen as an empirical rule that is able to predict the most abundant cage isomer for all the nitride EMFs known to date. Some EMF with M2 clusters, however, seem to escape this simple rule. We have proposed six large carbon cages (from C92 to C100) with sizeable (LUMO-4)–(LUMO-3) gaps and achievable energies as candidates for encapsulating metal nitride units or M2 clusters on condition that the formal six-electron transfer and other factors are accomplished. We have confirmed that the ionic model based on the formal transfer of four electrons from the encapsulated M2C2 carbide to the carbon cage is valid for the M2C2@C82 family. We have observed that the internal metal- carbide cluster is able to rotate inside the carbon cage. Using the aforesaid ionic model we have understood the higher stability of M2C2@C82 (C3v:8) when compared to carbide endohedrals with other IPR C82 isomers. The electrochemical properties for a series of EMFs have been studied theoretically. Analogously to the neutral M3N@Ih-C80 (M = Sc and Y) systems, rotation of the M3N unit inside the fullerene cage is predicted for the neutral, oxidized and reduced states of all the nitride EMFs with IPR cages studied through this work (from Sc3N@D5h-C80 to La3N@C96).

This dissertation addresses the exohedral cage functionalization and potential applications of the Sc₃N@C₈₀ and Sc₃N@C₇₈ trimetallic nitride endohedral metallofullerenes. In addition, this dissertation discusses miscellaneous research that is relevant to the aformentioned metallofullerenes and their applications, such as the discovery of a new cage isomer <i>(D_5h)</i> of Sc₃N@C₈₀, the synthesis of Lu₃N@C₈₀ as a novel X-ray contrasting agent, and the synthesis of Sc₃¹⁵N@C₈₀ with ¹⁵N₂ gas. The first derivative of Sc₃N@C₈₀ was synthesized by functionalizing the exterior of the cage via a [4 + 2] cycloaddition reaction with a ¹³C-labeled intermediate. Addition occurred across the [5,6] ring-juncture of the cage to form a mono-adduct, which has a mirror plane of symmetry as observed from the time-averaged ¹³C NMR spectrum. The structure of the mono-adduct was confirmed by X-ray crystallography. Diethyl and dibenzyl malonate adducts of Sc₃N@C₈₀ were synthesized, in addition to a ¹⁵N-labeled terminal amine derivative. Water-soluble metallofullerenols, Sc₃N@C₈₀(OH)_~10(O)_~10, were synthesized from polyanionic intermediates. The Sc₃N@C₇₈ metallofullerene was derivatized with a ¹³C-labeled reagent to afford mono-, di- and tri-adducts. A single structural isomer of the mono-adduct was found, while several isomers of the di- and tri-adducts were observed by HPLC. ¹³C and ¹H NMR data of the mono-adduct support a structure that results from addend addition to an asymmetric site on the C₇₈ carbon cage. The HPLC isolation and characterization of Lu₃N@C₈₀ is discussed. When irradiated with X-rays, Lu₃N@C₈₀ provided a small level of contrast that can only be attributed to the large atomic number (Z) of the lutetium atoms. Mixed-metal species that contains gadolinium and lutetium or holmium and lutetium could be employed as multifunctional contrasting agents for X-ray, MRI and radiopharmaceuticals, thereby eliminating the need for three separate agents. A new cage isomer of the Sc₃N@C₈₀ metallofullerene was synthesized and partially isolated by HPLC. This carbon cage possesses <i>D_5h</i> symmetry, as indicated by the time-averaged six line ¹³C NMR spectrum with a 1:2:2:1:1:1 ratio. The internal metal-nitride cluster of Sc₃N@C₈₀ was synthesized with a ¹⁵N-label for studying the motion(s) of the cluster (within the carbon cage) at various temperatures using ¹⁵N NMR spectroscopy. / Ph. D.

Endohedral metallofullerenes (EMF) have attracted increasing attention during past decades for their potential applications in the fields of biomedicine and nanomaterials. Trimetallic nitride template endohedral metallofullerenes (TNT EMFs) are some of the most promising fullerene-based materials (e.g., as MRI and X-ray contrast agents) because of their high yields compared to classic endohedral metallofullerenes. This dissertation addresses the chemical reactivity and regioselectivity of TNT EMFs. Based on the extraordinarily high stability of TNT EMFs relative to empty cage fullerenes and classic endohedral metallofullerenes, macroscopic quantities of high purity TNT EMFs were obtained directly from crude soot in a single facile step by using a cyclopentadiene-functionalized resin to trap the more reactive species via Diels-Alder reactions, allowing the TNT EMFs to pass through. We also developed a support-free chemical separation method of TNT EMFs from Sc- and Lu-based soot extract that makes use of the differing solubilities of unreacted TNT EMFs versus 9-methylanthracene-derivatized empty cage fullerenes. The exohedral functionalization of metallofullerenes can fine-tune their chemical and physical properties. The first N-methylpyrrolidino derivatives of TNT EMFs (Ih Sc3N@C80 and Ih Er3N@C80) were synthesized via 1,3-dipolar cycloaddition of N-methylazomethine ylides (Prato reaction). The demonstration of planar symmetry in the N-methylpyrrolidino derivatives by 13C NMR spectroscopy suggested that the reaction exclusively took place at the 5,6-ring junction. However, both 5,6-ring and 6,6 ring junction adducts were obtained when Ih Sc3N@C80 reacted with N-triphenylmethyl-5-oxazolidinone, as characterized by NMR spectroscopy and X-ray crystallography. The kinetically favored 6,6-ring junction adduct was converted to the thermodynamic product, the 5,6-ring junction adduct, upon thermal equilibration. The synthesis of pyrrolidino derivatives was also extended to two other Sc-based TNT EMFs, D5h Sc3N@C80 and Sc3N@C78. The reactivity and regioselectivity of D5h Sc3N@C80 and Sc3N@C78 were demonstrated by NMR spectroscopy, X-ray crystallography and theoretical calculations. Another type of reaction, the Bingel-Hirsch cyclopropanation was carried out with D3h Sc3N@C78 for the first time, yielding a single Cs-symmetric monoadduct and a dominant C2v-symmetric diadduct for the first time. The symmetric diadduct clearly demonstrates the remarkable regioselectivity control exerted by the encapsulated Sc3N cluster. We employed a LUMO electron density surface computational approach to predict multiadduct docking sites on the ellipsoidal fullerene cage surface. We also successfully synthesized the first derivative of a non-IPR fullerene, the diethyl malonate derivative of Sc3N@C68 by a Bingel-Hirsch reaction. The reactivity and regioselectivity of Sc3N@C68 were investigated by NMR spectroscopy and theoretical calculations. / Ph. D.

This thesis addresses the synthesis of a new mix-metal trimetallic nitride template endohedral metallofullerene (TNT-EMF) and the functionalizations of M3N@C80 (M = Sc, Gd, Ho) under the high-speed vibration milling (HSVM) condition. In addition, this thesis discusses the internal motion of the cluster, Sc3N inside three different carbon cages, C68, C78 and C80. Water-soluble derivatives of endohedral metallofullerenes possess a unique potential for medical applications, such as magnetic resonance imaging (MRI) contrast agents, X-ray contrast agents and nuclear medicine. The TNT-EMFs have inherent advantages over other endohedral metallofullerenes, such as M@C60 and M@C82, due to the encapsulation of up to three metal atoms inside the carbon cages. M3N@C80(OH)m(O)n (M = Sc, Gd, Ho) were synthesized under the HSVM condition and characterized by FT-IR, MALDI-TOF and XPS. The relaxivity studies on these water-soluble derivatives have shown that Gd-based metallofullerols have significantly higher relaxivities than commercially used MRI contrast agents (e.g. OmniscanTM) and can be the next generation MRI contrast agent. The Ho containing species has a high R2/R1 ratio compared to other samples showing the potential to be a T2 agent. In contrast to homonuclear M3N clusters, there is a paucity of mixed-metal cluster cases of TNT-EMFs reported to date because the mixed-metal metallofullerenes are difficult to be separated and purified. In this thesis, CeSc2N@C80 was synthesized, separated in pure form and fully characterized. Single-crystal X-ray diffraction shows that CeSc2N@C80 consists of a four atom asymmetric top (CeSc2N) inside a C80 (Ih ) carbon cage and the nitride ion is not located at the center of the carbon cage but is offset by 0.36 &Aring;. The NMR studies, together with the XPS results, show that CeSc2N@C80 is a weakly paramagnetic system with a single buried f electron spin. A new cage isomer of the Sc3N@C80 (D5h) metallofullerene was also isolated from the Ce-Sc mixture and the cage symmetry was confirmed by single-crystal X-ray diffraction. The internal motion of the metal-nitride cluster, Sc3N within the carbon cages (C68, C78 and C80) was studied at various temperatures using 45Sc NMR spectroscopy. The reorientation barriers (presumably dominated by motion internal to the cage) were calculated for these three TNT-EMFs. The preliminary results show that the quadrupole coupling constant of Sc3N@C80 (Ih) is quite close to that of Sc3N@C68. / Master of Science

Endohedral metallofullerenes (EMFs) have attracted increasing attention during past decades due to their novel structures and potential applications in a variety of fields such as biomedical applications and molecular electronics. This dissertation addresses the structural characterization and hydrogenation of EMFs. A family of novel large cage yttrium-based TNT EMFs Y₃N@C₂ₙ (n=40-44) was prepared, separated, and structurally characterized for the first time. The structure of Y₃N@C₂ₙ (n=40-44) is proposed by the experimental and computational ¹³C NMR studies. The first ⁸⁹Y NMR results for Y₃N@<I>Iₕ</i>-C₈₀, Y₃N@<I>Cₛ</i>-C₈₄ and Y₃N@<I>D₃</i>-C₈₆ reveal a progression from isotropic to restricted (Y₃N)⁶⁺</sup> cluster motional processes. The di-metallic EMF Y₂C₉₄ is distinguished as a metal-carbide based EMF, Y₂C₂@<I>D₃</i>-C₉₂. The carbide within the cage is successfully detected by ¹³C NMR. The scalar J_Y-C coupling between the yttrium atoms and the C₂ unit within the C₉₂ cage is successfully observed, suggesting the C₂ unit rotates rapidly around the yttrium atoms. Two paramagnetic endohedral metalloheterofullerenes, Y₂@C₇₉N and Gd₂@C₇₉N, were also synthesized and characterized. The EPR study demonstrated that the spin density is mainly localized between the two metallic ions. A spin-site exchange system could be constructed between Y₂@C₇₉N and the organic donor TMPD. Being a unique paramagnetic material, Gd₂@C₇₉N displays an unusual stability over a wide temperature range, which could be very useful in optical and magnetic areas. Functionalization of EMFs is another point of interest in this dissertation. Hydrogenated Sc₃N@C₈₀ was synthesized and characterized. Our study demonstrated that the Sc₃N@C₈₀ can be fully hydrogenated and the pristine Sc₃N@C₈₀ can be recovered from Sc₃N@C₈₀H₈₀ after being heated in vacuum. The hydrogenated EMFs could be potential hydrogen storage materials. / Ph. D.