Endohedral Metallofullerenes

Hisanori Shinohara Department of Chemistry, Nagoya University, Japan Nikos Tagmatarchis Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, Greece Foreword by Sir Harold Kroto

Foreword ix Preface xi

Personal Reflection – Nori Shinohara xiii

1 Introduction 1

1.1 The First Experimental Evidence of Metallofullerenes 1

1.2 Early Years of Metallofullerene Research 3

1.3 Conventional and IUPAC Nomenclature for Metallofullerenes 5

References 6

2 Synthesis, Extraction, and Purification 9

2.1 Synthesis of Endohedral Metallofullerenes 9

2.2 Solvent Extraction of Metallofullerenes from Primary Soot 14

2.3 Purification and Isolation by HPLC 15

2.4 Fast Separation and Purification with Lewis Acids 18

References 19

3 Molecular and Crystal Structures 23

3.1 Endohedral or Exohedral? A Big Controversy 23

3.2 Structural Analyses 25

References 37

4 Electronic States and Structures 43

4.1 Electron Transfer in Metallofullerenes 43

4.2 ESR Evidence on the Existence of Structural Isomers 45

4.3 Electrochemistry of Metallofullerenes 48

4.4 Similarity in the UV]Vis]NIR Absorption Spectra 51

4.5 Fermi Levels and the Electronic Structures 57

4.6 Metal–Cage Vibration within Metallofullerenes 59

References 63

5 Carbide and Nitride Metallofullerenes 69

5.1 Discovery of Carbide Metallofullerenes 69

5.2 Fullerene Quantum Gyroscope: An Ideal Molecular Rotor 75

5.3 Nitride Metallofullerenes 77

References 81

6 Non]Isolated Pentagon Rule Metallofullerenes 85

6.1 Isolated Pentagon Rule 85

6.2 Non]IPR Metallofullerenes 86

References 89

7 Oxide and Sulfide Metallofullerenes 91

7.1 O xide Metallofullerenes 91

7.2 Sulfide Metallofullerenes 95

References 100

8 Non]metal Endohedral Fullerenes 103

8.1 Nitrogen]Containing N@C60 103

8.2 Phosphorus]Containing P@C60 111

8.3 Inert Gas Endohedral Fullerenes He@C60, Ne@C60, Ar@C60, Kr@C60, and Xe@C60 112

8.4 Hydrogen]Containing H2@C60 120

8.5 Water]Containing H2O@C60 125

References 128

9 Scanning Tunneling Microscopy Studies of Metallofullerenes 133

9.1 STM Studies of Metallofullerenes on Clean Surfaces 133

9.2 Metallofullerenes as Superatom 135

9.3 STM/STS Studies on Metallofullerene Layers 137

9.4 STM/STS Studies on a Single Metallofullerene Molecule 139

References 141

10 Magnetic Properties of Metallofullerenes 145

10.1 Magnetism of Mono]metallofullerenes 145

10.2 SXAS and SXMCD Studies of Metallofullerenes 149

References 154

11 Organic Chemistry of Metallofullerenes 157

11.1 Cycloaddition Reactions 157

11.2 Radical Addition Reactions 178

11.3 Miscellaneous Reactions 180

11.4 Donor–Acceptor Dyads 185

11.5 Bis]adduct Formation 194

11.6 Supramolecular Functionalization 195

11.7 Purification of Metallofullerenes by Chemical Methods 198

References 200

12 Applications with Metallofullerenes 209

12.1 Solar Cells 209

12.2 Biomedical Aspects of Water]Soluble Metallofullerenes 221

References 226

13 Growth Mechanism 229

13.1 Carbon Clusters: A Road to Fullerene Growth 229

13.2 Roles Played by Metal Atoms in the Fullerene Growth 233

13.3 Top]Down or Bottom]Up Growth? 237

References 251

14 M@C60: A Big Mystery and a Big Challenge 255

14.1 What Happens to M@C60? 255

14.2 A Big Challenge: Superconductive Metallofullerenes 259

14.3 Future Prospects 261

References 262

Index 265