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A special issue of Inorganics (ISSN 2304-6740). This special issue belongs to the section "Inorganic Materials".

Deadline for manuscript submissions: 31 May 2024 | Viewed by 15032

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Special Issue Editors

Dr. Filip Uhlík

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Guest Editor

Department of Physical Chemistry, Faculty of Science, Charles University, 2030 Hlavova, Czech Republic
Interests: fullerenes; quantum chemistry; statistical thermodynamics; molecular simulations

Prof. Dr. Takeshi Akasaka

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Guest Editor

TARA Center, University of Tsukuba, Ibaraki 305-8577, Japan
Interests: chemistry of nanocarbons; endohedral metallofullerenes; fullerenes

Prof. Dr. Zdenek Slanina

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Guest Editor

Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ 85721-0041, USA
Interests: metallofullerenes; metal clusters; nanocarbons; fullerenes; theory and modeling; equilibrium and rate constants; stability evaluations; isomerism; nanoscience

Prof. Dr. Xing Lu

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Guest Editor

School of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China
Interests: fullerene; metallofullerene; crystallography; energy storage; nanomaterials

Special Issue Information

Dear Colleagues,

The 40th anniversary of the first experimental observation of fullerenes in a laser-vaporized graphite cluster beam mass spectrum, made by H. W. Kroto, J. R. Heath, S. C. O’Brien, R. F. Curl, and R. E. Smalley (DOI:10.1038/318162a0), is approaching. It will be the anniversary not only for fullerenes and buckminsterfullerene in particular, but also for the first endohedral metallofullerene observed, La@C60, just a few days later (DOI:10.1021/ja00311a102). There was tremendous progress in the field since then documented by tens of thousands of publications: The production of fullerenes in macroscopic quantities, i.e., hundreds of observed and isolated new species, has influenced their characterization both experimentally and theoretically, reaching various applications as MRI and X-ray contrast agents, radiotracers, photovoltaic cells, nanoelectronics, superconductors, and others.

The field of metallofullerene research is on the top with hundreds of new publications each year; in this Special Issue on Metallofullerenes in Inorganics, on the chemical and physical properties of metallofulleres, studied both experimentally and theoretically, is thus very timely.

Dr. Filip Uhlík
Prof. Dr. Takeshi Akasaka
Prof. Dr. Zdenek Slanina
Prof. Dr. Xing Lu
Guest Editors

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Keywords

metallofullerenes
endohedral fullerenes
nanomaterials
nanoelectronics

Published Papers (13 papers)

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Research

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14 pages, 4646 KiB

Open AccessArticle

On the Structural and Vibrational Properties of Solid Endohedral Metallofullerene Li@C₆₀

by Martina Vrankić, Takeshi Nakagawa, Melita Menelaou, Yasuhiro Takabayashi, Naoya Yoshikane, Keisuke Matsui, Ken Kokubo, Kenichi Kato, Saori Kawaguchi-Imada, Hirokazu Kadobayashi, John Arvanitidis, Yoshiki Kubota and Kosmas Prassides

Inorganics 2024, 12(4), 99; https://doi.org/10.3390/inorganics12040099 - 29 Mar 2024

Viewed by 593

Abstract

The endohedral lithium fulleride, Li⁺@C₆₀^•−, is a potential precursor for new families of molecular superconducting and electronic materials beyond those accessible to date from C₆₀ itself. Solid Li@C₆₀ comprises (Li@C₆₀)₂ dimers, isostructural and isoelectronic with the (C₅₉N)₂ units found in solid azafullerene. Here, we investigate the structural and vibrational properties of Li@C₆₀ samples synthesized by electrolytic reduction routes. The resulting materials are of high quality, with crystallinity far superior to that of their antecedents isolated by chemical reduction. They permit facile, unambiguous identification of both the reduced state of the fulleride units and the interball C-C bonds responsible for dimerization. However, severe orientational disorder conceals any crystal symmetry lowering due to the presence of dimers. Diffraction reveals the adoption of a hexagonal crystal structure (space group P6₃/mmc) at both low temperatures and high pressures, typically associated with close-packing of spherical monomer units. Such a situation is reminiscent of the structural behavior of the high-pressure Phase I of solid dihydrogen, H₂. Full article

(This article belongs to the Special Issue Research on Metallofullerenes)

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12 pages, 1784 KiB

Open AccessArticle

Stability and Electronic Properties of 1D and 2D Ca@C₆₀ Oligomers and Polymers

by Yabei Wu, Zhonghao Zhou and Zhiyong Wang

Inorganics 2024, 12(2), 45; https://doi.org/10.3390/inorganics12020045 - 29 Jan 2024

Viewed by 1214

Abstract

The polymerization of fullerenes is a significant method for obtaining fullerene-based materials that possess intriguing properties. Metallofullerenes, as a notable type of fullerene derivatives, are also capable of undergoing polymerization, potentially resulting in the creation of metallofullerene polymers. However, there is currently limited [...] Read more.

_{60}

as a representative compound to investigate the polymerization process of metallofullerenes. The objective of this research is to determine whether the polymerization process is energetically favorable and to examine how the electronic properties of the metallofullerene are altered throughout the polymerization process. Ca@C

_{60}

is a unique metallofullerene molecule that exhibits insolubility in common fullerene solvents like toluene and carbon disulfide but is soluble in aniline. This behavior suggests a potential tendency for Ca@C

_{60}

to form oligomers and polymers that resist dissolution. However, the structures and properties of polymerized Ca@C

_{60}

remain unknown. We employed density functional theory calculations to investigate the stability and electronic properties of one-dimensional and two-dimensional Ca@C

_{60}

oligomers and polymers. Our findings indicate that the coalescence of Ca@C

_{60}

monomers is energetically favorable, with a significant contribution from van der Waals interactions between the fullerene cages. The polymerization process of Ca@C

_{60}

also involves the formation of covalent linkages, including four-atom rings and C-C single bonds. The increase in the number of the Ca@C

_{60}

units to three and four in the oligomer leads to a significant decrease in the HOMO-LUMO gap. In the two-dimensional polymerized Ca@C

_{60}

, the organization of the monomers closely resembles the spatial configuration of carbon atoms in graphene. With a direct bandgap of 0.22 eV, the polymerized Ca@C

_{60}

holds potential for utilization in optoelectronic devices. Full article

(This article belongs to the Special Issue Research on Metallofullerenes)

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12 pages, 2944 KiB

Open AccessArticle

Geometries, Electronic Structures, Bonding Properties, and Stability Strategy of Endohedral Metallofullerenes TM@C₂₈ (TM = Sc⁻, Y⁻, La⁻, Ti, Zr, Hf, V⁺, Nb⁺, Ta⁺)

by Dong Liu, Yuan Shui and Tao Yang

Inorganics 2024, 12(2), 40; https://doi.org/10.3390/inorganics12020040 - 25 Jan 2024

Viewed by 1058

Abstract

We performed quantum chemical calculations on the geometries, electronic structures, bonding properties, and stability strategy of endohedral metallofullerenes TM@C₂₈ (TM = Sc⁻, Y⁻, La⁻, Ti, Zr, Hf, V⁺, Nb⁺, Ta⁺). Our calculations revealed that there are three different lowest-energy structures with C_2v, C_3v, and T_d symmetries for TM@C₂₈. The HOMO–LUMO gap of all these structures ranges from 1.35 eV to 2.31 eV, in which [V@C₂₈]⁺ has the lowest HOMO–LUMO gap of 1.35 eV. The molecular orbitals are mainly composed of fullerene cage orbitals and slightly encapsulated metal orbitals. The bonding analysis on the metal–cage interactions reveals they are dominated by the Coulomb term ΔE_elstat and the orbital interaction term ΔE_orb, in which the orbital interaction term ΔE_orb contributes more than the Coulomb term ΔE_elstat. The addition of one or two CF₃ groups to [V@C₂₈]⁺ could increase the HOMO–LUMO gap and further increase the stability of [V@C₂₈]⁺. Full article

(This article belongs to the Special Issue Research on Metallofullerenes)

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11 pages, 1930 KiB

Open AccessArticle

Synthesis and Characterization of a Novel Non-Isolated-Pentagon-Rule Isomer of Th@C₇₆:Th@C₁(17418)-C₇₆

by Yunpeng Xia, Yi Shen, Yang-Rong Yao, Qingyu Meng and Ning Chen

Inorganics 2023, 11(11), 422; https://doi.org/10.3390/inorganics11110422 - 25 Oct 2023

Cited by 1 | Viewed by 1157

Abstract

A novel Non-Isolated-Pentagon-Rule (non-IPR) isomer of thorium-based endohedral mono-metallofullerenes (mono-EMFs), Th@C₁(17418)-C₇₆, was successfully synthesized and characterized using MALDI-TOF mass spectroscopy, single-crystal X-ray diffraction, UV-vis-NIR spectroscopy, and Raman spectroscopy. The molecular structure of this non-IPR isomer was determined unambiguously as Th@C₁(17418)-C₇₆ using a single-crystal X-ray diffraction analysis. The crystallographic results further revealed that the optimal Th site resided at the intersection of two adjacent pentagons, similar to that of U@C₁(17418)-C₇₆. Additionally, the UV-vis-NIR spectra of Th@C₁(17418)-C₇₆ exhibited distinct differences compared to the previously reported U@C₁(17418)-C₇₆, highlighting the distinctive electronic structure of actinium-based endohedral metallofullerenes (EMFs). The Raman spectrum of Th@C₁(17418)-C₇₆ exhibited similarities to that previously reported for thorium-based EMFs, indicating the analogous strong metal–cage interactions of thorium-based EMFs. Full article

(This article belongs to the Special Issue Research on Metallofullerenes)

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14 pages, 4116 KiB

Open AccessArticle

Reactivity of Open-Shell Metallofullerene Anions: Synthesis, Crystal Structures, and Electrochemical Properties of Benzylated Gd@C_2v-C₈₂

by Xinyi Zhou, Yang-Rong Yao, Yajing Hu, Le Yang, Shaoting Yang, Yilu Zhang, Qianyan Zhang, Ping Peng, Peng Jin and Fang-Fang Li

Inorganics 2023, 11(9), 349; https://doi.org/10.3390/inorganics11090349 - 25 Aug 2023

Cited by 2 | Viewed by 1110

Abstract

The reactivity of the open-shell Gd@C_2v-C₈₂ with different charge states towards benzyl bromide was investigated. [Gd@C_2v-C₈₂]³⁻ exhibited enhanced activity relative to Gd@C_2v-C₈₂ and [Gd@C_2v-C₈₂]⁻. The structural characterizations, including MALDI-TOF MS, UV-vis-NIR, and single crystal X-ray diffraction, indicate the formation of isomeric benzyl monoadducts of Gd@C_2v-C₈₂. All three monoadducts contain 1:1 mirror-symmetric enantiomers. Additionally, the addition of the benzyl group and its specific position result in distinct electrochemical behavior of the products compared to the parent Gd@C_2v-C₈₂. Theoretical studies demonstrate that only [Gd@C_2v-C₈₂]³⁻ has a HOMO energy level that matches well with the LUMO energy level of the PhCH₂ radical, providing a rationalization for the observed significantly different reactivity. Full article

(This article belongs to the Special Issue Research on Metallofullerenes)

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13 pages, 2891 KiB

Open AccessArticle

TmCN@C₈₂: Monometallic Clusterfullerene Encapsulating a Tm³⁺ Ion

by Huichao Zhang, Jinpeng Xin, Huaimin Jin, Wenhao Xiang, Muqing Chen, Yang-Rong Yao and Shangfeng Yang

Inorganics 2023, 11(8), 323; https://doi.org/10.3390/inorganics11080323 - 31 Jul 2023

Cited by 1 | Viewed by 1142

Abstract

Metal cyanide clusterfullerenes (CYCFs) are formed via the encapsulation of a single metal atom and a cyanide unit inside fullerene cages, endowing them with excellent properties in various applications. In this work, we report the synthesis, isolation, and characterizations of the first cases of thulium (Tm)-based CYCFs with the popular C₈₂ carbon cages. The structural elucidation of the two TmCN@C₈₂ isomers was achieved via diverse analytical techniques, including mass spectrometry, Vis-NIR spectroscopy, single-crystal X-ray crystallography, and cyclic voltammetry. The crystallographic analyses unambiguously confirmed the molecular structures of the two TmCN@C₈₂ isomers as TmCN@C_s(6)-C₈₂ and TmCN@C_2v(9)-C₈₂. Both TmCN clusters adopt a well-established triangular configuration, with the Tm ion located on the symmetrical plane of the carbon cages. The electronic structures of both TmCN@C₈₂ isomers adopt a Tm³⁺(CN)⁻@(C₈₂)²⁻ configuration, exhibiting characteristic spectral and electrochemical properties reminiscent of divalent endohedral metallofullerenes (EMFs). Intriguingly, unlike the divalent Tm²⁺ ion observed in the mono-metallofullerenes Tm@C_2n, a higher oxidation state of Tm³⁺ is identified in the monometallic TmCN cluster due to bonding with the cyanide anion. This result provides valuable insight into the essential role of the non-metallic endo-units in governing the oxidation state of the metal ion and the electronic behaviors of EMFs. Full article

(This article belongs to the Special Issue Research on Metallofullerenes)

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9 pages, 958 KiB

Open AccessArticle

Pr@C₈₂ Metallofullerene: Calculated Isomeric Populations

by Zdeněk Slanina, Filip Uhlík, Takeshi Akasaka, Xing Lu and Ludwik Adamowicz

Inorganics 2023, 11(7), 313; https://doi.org/10.3390/inorganics11070313 - 24 Jul 2023

Viewed by 853

Abstract

Relative equilibrium populations of the five lowest-energy isolated-pentagon-rule (IPR) isomeric structures of Pr@C

_{82}

under high-temperature fullerene synthesis conditions were calculated with the Gibbs energy terms based on molecular characteristics derived using density functional theory (DFT) treatments (B3LYP/6-31+G

^{*}

∼SDD energetics and B3LYP/6-31G [...] Read more.

Relative equilibrium populations of the five lowest-energy isolated-pentagon-rule (IPR) isomeric structures of Pr@C

_{82}

^{*}

∼SDD energetics and B3LYP/6-31G

^{*}

∼SDD entropy). Two leading isomers were identified, major Pr@

C_{2 v}; 9

-C

_{82}

and minor Pr@

C_{s}; 6

-C

_{82}

. The calculated isomeric relative equilibrium populations agreed with observations. Full article

(This article belongs to the Special Issue Research on Metallofullerenes)

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9 pages, 2817 KiB

Open AccessArticle

Lu-Lu Bond in Lu₂@C₆₀ Metallofullerenes

by Yaoxiao Zhao, Wangqiang Shen, Weixing Chen and Xing Lu

Inorganics 2023, 11(7), 277; https://doi.org/10.3390/inorganics11070277 - 28 Jun 2023

Viewed by 1026

Abstract

This study on Lu₂@C₆₀ isomers provides insights into the metal–metal bond through the confinement effect of fullerene cages. Density functional theory calculations were used to study the nature of the Lu-Lu bond in two stable endohedral metallofullerenes (EMFs), Lu₂@C_2v_C₆₀ and Lu₂@I_h_C₆₀, both with negative endohedral energy. These two isomers are geometrically connected through a simple Stone–Wales (SW) transformation. The electronic configuration of (Lu₂)⁴⁺@C₆₀⁴⁻ was also confirmed, leading to the formation of a two-center two-electron (2c–2e) Lu-Lu σ single bond. By comparing the Lu-Lu bonds in Lu₂@C₆₀ with those in acknowledged Lu₂@C_2n, the smaller C₆₀ fullerene compressed the geometry of Lu₂ resulting in a much shorter Lu-Lu bond length. However, the Lu-Lu bond strength is slightly weaker in Lu₂@C₆₀ than that in large fullerenes, as the Lu-Lu bond in C₆₀ is likely a p-p σ bond with an above the 40% contribution of p orbital and a strong metal–cage interaction. Additionally, the vis-NIR spectra of Lu₂@C_2v_C₆₀ and Lu₂@I_h_C₆₀ were simulated, which could provide valuable information for future experimental studies on Lu-based EMFs. Full article

(This article belongs to the Special Issue Research on Metallofullerenes)

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15 pages, 3040 KiB

Open AccessArticle

DFT Analysis of the Electronic and Structural Properties of Lanthanide Nitride Cluster Fullerenes Ln₃N@C₈₀

by César Martínez-Flores and Vladimir A. Basiuk

Inorganics 2023, 11(5), 223; https://doi.org/10.3390/inorganics11050223 - 22 May 2023

Viewed by 1175

Abstract

We have undertaken a DFT study of the nitride cluster fullerenes (NCFs) Ln₃N@C₈₀ for the complete series of fourteen lanthanides plus lanthanum by using the PBE functional with the Grimme’s dispersion correction (PBE-D2). We tested the DN and DND basis sets, which are equivalent to 6-31G and 6-31G(d) Pople-type basis sets, respectively. Due to the known convergence problems when treating lanthanide-containing systems, only with the DN basis set was it possible to complete the calculations (geometry optimization and analysis of selected electronic parameters) for all the fifteen NCFs. We found that the bending of the Ln₃N cluster increases as the ionic radius increases, in general agreement with the available X-ray diffraction data. The Ln₃N cluster becomes more planar as the Ln–N bond length is contracted, and the C₈₀ cavity slightly deforms. The HOMO-LUMO energies and distribution, as well as the charge and spin of the encapsulated metal ions, are analyzed. Full article

(This article belongs to the Special Issue Research on Metallofullerenes)

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Review

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18 pages, 4189 KiB

Open AccessReview

Endometallofullerenes in the Gas Phase: Progress and Prospect

by Yameng Hou and Xianglei Kong

Inorganics 2024, 12(3), 68; https://doi.org/10.3390/inorganics12030068 - 23 Feb 2024

Viewed by 870

Abstract

This review describes the progress of the gas-phase study of endometallofullerenes (EMFs) by mass spectrometry and theoretical calculation over the past 15 years. The attention herein focuses on the gas-phase syntheses, reactions, and generation mechanisms of some novel EMF ions, along with their structures and properties. The highlighted new species include EMFs with small-size carbon cages of C_2n (n < 60), multiple metal atoms (M_x@C_2n, x ≥ 3), late transition metals, and encaged ionic bonds. Furthermore, the gas-phase experimental and calculational supports for top-down or bottom-up models are summarized and discussed. These gas-phase results not only provide experimental evidence for the existence of related novel EMF species and possible synthesis methods for them, but they also provide new insights about chemical bonds in restricted space. In addition, the opportunities and further development directions faced by gas-phase EMF study are anticipated. Full article

(This article belongs to the Special Issue Research on Metallofullerenes)

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15 pages, 2248 KiB

Open AccessReview

Capturing Unstable Metallofullerenes

by Fupin Liu and Alexey A. Popov

Inorganics 2024, 12(2), 48; https://doi.org/10.3390/inorganics12020048 - 31 Jan 2024

Viewed by 1224

Abstract

Metallofullerenes are interesting molecules with unique structures and physicochemical properties. After they are formed in the arc-discharge process, they are first buried in the carbon soot, which requires solvent extraction to fish them out, normally followed by HPLC separation. In this minireview, we summarize the main procedures developed to obtain pure metallofullerenes, including well-established extraction with conventional fullerene solvents followed by HPLC (procedure (I) as well as several methods developed for isolation and purification of unstable fullerenes insoluble in conventional fullerene solvents, including chemical modification followed by dissolution (II.1), chemical functionalization during extraction followed by HPLC (II.2), and chemical functionalization of ionic EMFs after redox-extraction followed by HPLC (procedure II.3). The main focus here is on procedure II.3, for which the current status and future perspective are discussed. Full article

(This article belongs to the Special Issue Research on Metallofullerenes)

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20 pages, 2978 KiB

Open AccessReview

Process Parameter Optimisation for Endohedral Metallofullerene Synthesis via the Arc-Discharge Method

by Sapna Sinha, Karifa Sanfo, Panagiotis Dallas, Sujay Kumar and Kyriakos Porfyrakis

Inorganics 2024, 12(2), 38; https://doi.org/10.3390/inorganics12020038 - 25 Jan 2024

Viewed by 1401

Abstract

Fullerenes have a unique structure, capable of both encapsulating other molecules and reacting with those on the exterior surface. Fullerene derivatives have also been found to have enormous potential to address the challenges of the renewable energy sector and current environmental issues, such as in the production of n-type materials in bulk heterojunction solar cells, as antimicrobial agents, in photocatalytic water treatment processes, and in sensor technologies. Endohedral metallofullerenes, in particular, can possess unpaired electron spins, driven by the enclosed metal atom or cluster, which yield valuable magnetic properties. These properties have significant potential for applications in molecular magnets, spin probes, quantum computing, and devices such as quantum information processing,, atomic clocks, and molecular magnets. However, the intrinsically low yield of endohedral fullerenes remains a huge obstacle, impeding not only their industrial utilization but also the synthesis and characterization essential for exploring novel applications. The low yield and difficulty in separation of different types of endohedral fullerenes results in the usage of a large amount of solvents and energy, which is detrimental to the environment. In this paper, we analyse the methodologies proposed by various researchers and identify the critical synthesis parameters that play a role in increasing the yields of fullerenes. Full article

(This article belongs to the Special Issue Research on Metallofullerenes)

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20 pages, 3411 KiB

Open AccessReview

Recent Progress on the Functionalization of Endohedral Metallofullerenes

by Song Wang, Xianming Zhang, Xi Tan, Hongzhen Li, Songxin Dai, Bin Yao, Xingyan Liu, Youzhou He and Fei Jin

Inorganics 2023, 11(8), 346; https://doi.org/10.3390/inorganics11080346 - 21 Aug 2023

Cited by 1 | Viewed by 1108

Abstract

Functionalization of endohedral metallofullerenes (EMFs) plays an important role in exploring the reactivity of EMFs and stabilizing missing EMFs, thus conferring tunable properties and turning EMFs into applicable materials. In this review, we present exhaustive progress on the functionalization of EMFs since 2019. Classic functionalization reactions include Prato reactions, Bingel–Hirsch reactions, radical addition reactions, carbene addition reactions, and so on are summarized. And new complicated multi-component reactions and other creative reactions are presented as well. We also discuss the structural features of derivatives of EMFs and the corresponding reaction mechanisms to understand the reactivity and regioselectivity of EMFs. In the end, we make conclusions and put forward an outlook on the prospect of the functionalization of EMFs. Full article

(This article belongs to the Special Issue Research on Metallofullerenes)

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