Endohedral Dimetallofullerene Research Articles

Imaging the Single-Electron Ln-Ln Bonding Orbital in a Dimetallofullerene Molecular Magnet.

Chemically robust single-molecule magnets (SMMs) with sufficiently high blocking temperatures TB are among the key building blocks for the realization of molecular spintronic or quantum computing devices. Such device applications require access to the magnetic system of a SMM molecule by means of electronic transport, which primarily depends on the interaction of magnetic orbitals with the electronic states of the metallic electrodes. Scanning tunneling microscopy in combination with ab initio calculations allows to directly address the unoccupied component of the single-electron molecular orbital that mediates the ferromagnetic exchange coupling between two 4f ions within a lanthanide endohedral dimetallofullerene deposited on a graphene surface. The single-electron metal-metal bond provides a direct access to the molecule's magnetic system in the transport experiments, paving the way for investigation and controlled manipulation of the spin system of individual dimetallofullerene SMMs, essential for molecularspintronics.

Unusually large hyperfine structure of the electron spin levels in an endohedral dimetallofullerene and its spin coherent properties.

We report the synthesis, ESR spectroscopic and spin coherent properties of the dimetallofullerene Sc2@C80(CH2Ph). The single-electron metal-metal bond of the Sc2 dimer inside the fullerene's cage is stabilized with the electron spin density being fully localized at the metal bond. This results in an extraordinary strong hyperfine interaction of the electron spin with the 45Sc nuclear spins with a coupling constant a = 18.2 mT (∼510 MHz) and yields a fully resolved hyperfine-split ESR spectrum comprising 64 lines. The splitting is present even at low temperatures where the molecular dynamics are completely frozen. The large extent and the robustness of the hyperfine-split spectra enable us to identify and control the well-defined transitions between specific electron-nuclear quantum states. This made it possible to demonstrate in our pulse ESR study the remarkable spin coherent dynamics of Sc2@C80(CH2Ph), such as the generation of arbitrary superpositions of the spin states in a nutation experiment and the spin dephasing times above 10 μs at temperatures T < 80 K reaching the value of 17 μs at T ≤ 20 K. These observations suggest Sc2@C80(CH2Ph) as an interesting qubit candidate and motivate further synthetic efforts to obtain fullerene-based systems with superior spin properties.

Unmasking the Optimal Isomers of Ti2C84: Ti2C2@C82 Instead of Ti2@C84

Up to now, the controversies over the stable structures of endohedral di-metallofullerenes M2Cn, whether M2@Cn or M2C2@Cn–2, have continued ceaselessly. Herein, to disclose the optimal structures o...

Experimental and Theoretical Investigation on the Molecular Structures of Pr@C72, Pr2@C72 and and Their Functionalized Adducts

A novel Pr-based mono-metallofullerene derivative, Pr@C72(C6H3Cl2), was successfully prepared and isolated and its molecular structure was verified as Pr@C2(10612)-C72(C6H3Cl2) by combined UV-visible-near-infrared absorption spectroscopy and quantum mechanics characterization, as well as a comparison with the structurally characterized analogue La@C72(C6H3Cl2). Furthermore, an additional computation indicated that the pristine Pr@C72 has the lowest-lying structure as Pr@C2(10612)-C72, followed by Pr@C2v(11188)-C72, which lies only 0.62 kcal mol-1 above Pr@C2(10612)-C72. The charge transfer and orbital interaction between the endohedral Pr atom and the carbon cage as well as the electronic configuration and formal charge state of the encapsulated Pr atom temperature dependence of their thermodynamic distribution was also estimated based on the computed quantum mechanics data. The pristine endohedral d-imetallofullerene Pr2@C72 was prepared and isolated [2]. Its structure was determined to be Pr2@D2(10611)-C72 by a combination of mass spectrometry, UV-visible-near-infrared absorption spectroscopy, and quantum mechanics characterization. Moreover, the reactivity of Pr2@D2(10611)-C72 was probed by 2-adamantane-2,3-[3H]-diazirine functionalization, and the resulting adducts were identified with mass spectrometry and high performance liquid chromatography. Additionally, the preferred addition positions and isomeric structures of the dominant mono-adduct Pr2@C72(Ad) were further investigated using density functional theory.

Synthesis and Photoinduced Electron-Transfer Reactions in a La2 @Ih -C80 -Phenoxazine Conjugate.

A newly designed electron donor-acceptor conjugate consisting of an endohedral dimetallofullerene (La2 @Ih -C80 ) and phenoxazine (POZ) was successfully synthesized under Prato conditions. Our results document that the 1,3-dipolar cycloaddition took place across the [5,6] junction to afford exclusively the corresponding [5,6] cycloadduct. The structure of the conjugate was characterized by means of NMR spectroscopy, absorption spectroscopy, and electrochemical studies. Computational calculations suggest that the electron density of the highest occupied molecular orbital (HOMO) is distributed on the POZ moiety, whereas that of the lowest unoccupied molecular orbital (LUMO) is located at the endohedral La atoms, leading to efficient separation of the HOMO and LUMO in the conjugate. Time-resolved absorption spectroscopic investigations and spectroelectrochemical measurements corroborate the formation of the energetically low-lying (La2 @Ih -C80 ).- -(POZ).+ radical-ion-pair state by means of ultrafast through-space electron transfer.

Strong electronic coupling and electron transfer in a Ce2@Ih-C80–H2P electron donor acceptor conjugate

A newly designed electron donor-acceptor conjugate, namely Ce2@Ih-C80-H2P consisting of an endohedral dimetallofullerene Ce2@Ih-C80 and a free-base prophyrin (H2P), has been synthesized and systematically investigated. Basic characterization by means of NMR spectroscopy, steady-state absorption spectroscopy, and electrochemistry points to a folded configuration with sizeable interactions between Ce2@Ih-C80 and H2P. Complementary DFT optimization also results in the same conclusions. Time-resolved absorption spectroscopic investigations corroborate the formation of the (Ce2)˙(-)@Ih-C80-(H2P)˙(+) radical ion pair state in non-polar as well as polar media. Overall, the modus operandi is an ultrafast through-space electron transfer enabled by the folded configuration in the ground and excited state.

On exchange coupling and bonding in the Gd2@C80 and Gd2@C79N endohedral dimetallo-fullerenes

A series of computational experiments performed with various methods belonging to wave-function and density functional theories approaches the issue of bonding regime and exchange coupling in the title compounds. Gd2@C80 is computed with a very weak exchange coupling, the sign depending on the method, while Gd2@C79N has resulted with a strong coupling and ferromagnetic ground state, irrespective of the computational approach. The multi-configuration calculation and broken symmetry estimation are yielding closely coincident coupling constants, of about J ∼ 400 cm−1. No experimental estimation exists, but the ferromagnetic ground state of Gd2@C79N is confirmed from paramagnetic resonance data. The different behaviour is due to particularities of electron accommodation in the orbital scheme. The exchange effects localised on atom lead to preference for parallel alignment of the electrons placed in the 4f and 5d lanthanide shells, determining also a ferromagnetic inter-centre coupling. The structural insight is completed with a ligand field analysis of the density functional theory results in the context of frozen density embedding. The energy decomposition analysis of bonding effects is also discussed. Finally, with the help of home-made codes (named Xatom+Xsphere), a model for the atom encapsulated in a cage is designed, the exemplified numeric experiments showing relevance for the considered endohedral metallo-fullerene issues.

Thermal Carbosilylation of Endohedral Dimetallofullerene La2@Ih-C80 with Silirane

Thermal carbosilylation of endohedral dimetallofullerene La(2)@I(h)-C(80) with silirane (silacyclopropane) is reported herein for the first time. Two diastereomers of the carbosilylated La(2)@I(h)-C(80) have been isolated and characterized. The fascinating molecular structure of one diastereomer of the carbosilylated derivatives has been determined unambiguously using X-ray crystallographic analysis. Detailed characteristics of the molecular structures including their metal atom movements have also been revealed using NMR spectroscopic studies and computational calculations. Results revealed that two La atoms move dynamically inside the carbon sphere. Furthermore, electrochemical study has demonstrated that carbosilylation is effective to fine-tune the La(2)@I(h)-C(80) electronic properties.

The Computational Vibrational and Ultraviolet Spectra Study of Endohedral Dimetallofullerene La&lt;SUB&gt;2&lt;/SUB&gt; @ C&lt;SUB&gt;80&lt;/SUB&gt;

The Computational Vibrational and Ultraviolet Spectra Study of Endohedral Dimetallofullerene La&lt;SUB&gt;2&lt;/SUB&gt; @ C&lt;SUB&gt;80&lt;/SUB&gt;

Spectroscopic and Theoretical Study of Endohedral Dimetallofullerene Having a Non-IPR Fullerene Cage: Ce2@C72

The endohedral dimetallofullerene having a non-IPR fullerene cage, Ce2@C72, is spectroscopically and theoretically characterized. The (13)C NMR measurements display large temperature-dependent signals caused by paramagnetic shifts, indicating that the Ce atoms are located near the two fused pentagons in the C72 cage. Theoretical calculations are performed to clarify the metal position, which are in good agreement with the result obtained by the paramagnetic (13)C NMR analysis. Electrochemical measurements reveal that Ce2@C72 has particularly lower oxidation and higher reduction potentials than other endohedral dimetallofullerenes.

Synthesis of endohedral di-and monometallofullerenes Y2@C84, Ce2@C78, and M@C82 (M = Y, Ce)

Endohedral metallofullerenes Y2@C84, Ce2@C78, and M@C82 (M = Y, Ce) were synthesized by the electric arc method and isolated from the soot using extraction with o-dichlorobenzene. Pure (98%) endohedral dimetallofullerenes Y2@C84 and Ce2@C78 were isolated for the first time from o-dichlorobenzene extracts using HPLC and characterized by mass spectrometry and spectrophotometry.

Proof for trivalent Sc ions inSc2@C84from high-energy spectroscopy

The electronic structure and the valency of the Sc ions in the endohedral dimetallofullerene ${\mathrm{Sc}}_{2}@{\mathrm{C}}_{84}$ with ${D}_{2d}$ symmetry are probed using high-energy spectroscopy. Comparison of the Sc $2\stackrel{\ensuremath{\rightarrow}}{p}3d$ x-ray-absorption spectrum with calculated ionic multiplet spectra shows that the Sc ions are trivalent. Detailed multiplet calculations including covalency indicate that the effective valency of the Sc(III) ions can be described by a formal charge transfer to the fullerene cage of $2.6\ifmmode\pm\else\textpm\fi{}0.1.$ This illustrates that a purely ionic picture is not valid for the electronic structure of ${\mathrm{Sc}}_{2}@{\mathrm{C}}_{84},$ and that a more complex picture including finite hybridization between the Sc and the fullerene cage has to be applied.

Vibrational Spectroscopy of Endohedral Dimetallofullerene, La2@C80

Abstract The first FT-IR spectra of La2@C80 are observed at temperatures from 353 to 83 K by dispersing the sample into the KBr pellet, which confirm that the C80 cage has Ih symmetry, as supported from theoretical calculations. Also discussed is the rotational motion of the C80 cage.

Structural study of endohedral dimetallofullerenes Sc2@C84 and Sc2@C74

Structural study of endohedral dimetallofullerenes Sc2@C84 and Sc2@C74

Recent progress in endohedral dimetallofullerenes

Encapsulation of two metal atoms inside hollow fullerene cages is of current interest since new spherical cage molecules are formed. The isolation and purification of endohedral dimetallofullerenes such as La 2@C 80 and Sc 2@C 84 in macroscopic quantities have made it possible to investigate the structures, properties and chemical reactivities. Recent progress in the theoretical and experimental studies is summarized.

Structures and electronic states of endohedral dimetallofullerenes: M2@C80 (M = Sc, Y, La, Ce, Pr, Eu, Gd, Yb and Lu)

Encapsulation of group 3 and lanthanide metals inside C80 isomers is investigated using ab initio molecular orbital and non-local density functional methods. The stability and structures depend on the properties of the metal. It is suggested that an energetically stable structure (with a large HOMO-LUMO gap) is most abundantly produced.

Endohedral dimetallofullerenes Sc 2@C 84 and La 2@C 80. Are the metal atoms still inside the fullerence cages?

In order to provide insight into the motion of metal atoms in endohedral dimetallofullerenes, Sc 2@C 84 and La 2@C 80 are investigated as typical examples by use of ab initio molecular orbital and nonlocal density functional methods. It is suggested that the two Sc atoms can oscillate with considerable amplitude while the two La atoms can circulate inside the fullerene cage with small barriers of ≈ 5 cal/mol. It is expected that such metal motions will lead to interesting electronic and magnetic properties.

Theoretical study of the dimetallofullerene Sc 2@C 84

In order to extend the knowledge of endohedral dimetallofullerenes, the electronic structures and properties of Sc 2@C 84 are investigated as a typical example by means of ab initio calculations. The electronic structure is formally described as (Sc 2+) 2C 84 4− as a result of the transfer of almost four electrons from Sc 2 to C 84. It is suggested that the resultant two Sc 2+ dications are strongly bound to the double bonds and hexagonal rings in the most abundant D 2d and D 2 isomers of C 84, respectively, with long Sc-Sc distances.