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FT This copy has been deposited in the Library of O C- ^— This copy has been deposited in the Senate House Library, Senate House, Malet Street, London WC1E 7HU. -------------- nders 020 8992 3965 Metal-Ammonia-Fulleride Solutions dznznzzzzziUCL i i University College London A thesis submitted in accordance with the requirements of the University of London for the degree of Doctor of Philosophy Christopher Anthony Howard January 2005 UMI Number: U592965 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. Dissertation Publishing UMI U592965 Published by ProQuest LLC 2013. Copyright in the Dissertation held by the Author. Microform Edition © ProQuest LLC. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code. ProQuest LLC 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 11 Abstract This project is the first concerted effort to study the structure of metal-ammonia- fulleride solutions. These novel solutions contain high concentrations of fulleride anions, C6on~ (n = 1 to 5). A detailed understanding of the solubility of fullerenes and their derivatives has long been sought after: something this project addresses. The work focuses on the structure of the solutions using the complementary techniques of wide angle neutron diffraction, Small Angle Neutron Scattering (SANS), and Monte Carlo simulations. A highly developed structure is found over the short and intermediate length scales. The results show concentrated solutions of solvent separated, strongly coordinated, fulleride anions, maintained by an intriguing reorganisation of the ammonia solvent around the anions in solution. In more detail, we find two solvation shells around the C6o anions containing around -45 and -80 ammonia molecules respectively. The ammonia solvent molecules direct one of their hydrogen atoms towards the centre of the Cco anions, allowing the other two hydrogen atoms to complete hydrogen-bonds within and across the shells. The solvation structure of the cation in solution is found to be very similar to its solvation structure in bulk metal-ammonia solutions. The structure and stability of the solutions is found to be dependent on both anionic charge and cation charge density. The scientific importance of the solutions is demonstrated by the attainment of high quality 13C NMR spectra for the fulleride anions CaT (w = 1 to 5) for the first time in an identical solvent. Previous limitations of low concentrations, poor quality samples, and restrictions due to the air sensitivity of the anions have been overcome. The data here includes the first 13C NMR spectrum of C6o5’. These data reveals that all the carbon atoms have an identical electronic environment in this anion. Acknowledgements I would like first and foremost to thank my supervisor Neal Skipper for his guidance, encouragement and friendship over the course of my PhD. A big thank you must also go to Jonathan Wasse and Helen Thompson for their help, expertise and advice throughout. Particular mention must also be given to Tom Weller for his inspirational, daily enthusiasm for science and to Cecilia Gejke, Arthur Lovell and Mark Ellerby for their friendship and assistance on experiments and in the laboratory. Also thanks to Hayley Spiers, Jon Allen, Helen Walker, Ross Springell and Eamonn Beime at UCL. I would like to thank the instrument scientists and sample environment staff who have helped me in this work: Daniel Bowron, Alan Soper, Richard Heenan, Steve King, John Dreyer, Chris Goodway and Mike Yates at ISIS, and Charles Dewhurst and Pierre Palleau at the ILL. Thanks also to Peter Edwards, Matt Lodge and Nick Rees at Oxford for their help with the NMR measurements. I would also like to thank Merck Chemical Ltd. for a CASE award and to Rod Riddle for his help and advice. Finally, I must thank my parents for their unconditional support and encouragement throughout my life. And, of course, a big special thank you to Debbie White for her unstinting patience, good spirit, friendship and love. Contents Abstract iii Acknowledgements iv Contents v List of Figures x List of Tables xvii Introduction 1 Scope of Thesis 2 Chapter I Background and Motivation 4 1.1 C6o Structure 4 1.2 The Electronic Structure of Buckminster Fullerene, C6o 6 1.3 Higher Fullerenes and More New Allotropes of Carbon 9 1.4 Applications of Fullerenes 11 1.5 Motivation for Solution Studies of Fullerenes 11 1.5.1 Separation/Purification o f Fullerenes 12 1.5.2 Chemical Manipulation 13 1.5.3 Thin Film Deposition 13 1.5.4 A Medium for Studying Fulleride Ions 15 1.6 Fullerenes in Solution: Previous Work 15 1.6.1 Routes to Solubilisation 16 1.7 The Route to Dissolution 17 1.7.1 Metal-ammonia Solutions 17 1.7.2 Metal-Ammonia-Fulleride Solutions: Previous Work 19 v 1.7.3 Ammonia as a Solvent 19 1.8 Doped Fullerenes and Superconductivity 21 1.8.1 Ammoniation of theCw Salts 24 Chapter 2 The Theory of Neutron Scattering 26 2.1 Introduction 26 2.2 Neutron Properties 27 2.2 Definitions 29 2.2.1 The Scattering Vector, Q 29 2.2.2 Differential Cross Sections 30 2.3 Scattering of Neutrons from a Bound Nucleus 31 2.4 Scattering from a General System of Particles 32 2.5 Coherent and Incoherent Scattering 36 2.6 Diffraction Measurements 38 2.7 Faber-Ziman Formalism 39 2.8 Small Angle Neutron Scattering 40 2.9 Second Order Isotopic Substitution 41 Chapter 3 Experimental Details and Data Reduction 44 3.1 Introduction 44 3.2 Sample Preparation: Generic 46 3.2.1 Cfio, Fullerene 46 3.2.2 Preparing the Gas Handling Equipment 46 3.2.3 Purification o f Ammonia Solvent 48 3.2.4 Loading 49 3.2.5 Calculating the Amount of Gas Required 49 3.2.6 Condensation o f the Solvent 50 3.2.7 AxCfio Salts 51 3.3 Neutron Scattering 51 3.3.1 Neutron Production 51 vi 3.3.1.1 Neutron Production: Spallation 52 3.3.1.2 Reactor Source 53 3.3.2 The SANDALS Instrument 54 3.3.2.1 SANDALS Sample Environment 54 3.3.3 SANDALS Data Reduction 56 3.3.4 The D22 Instrument 59 3.3.5 D22 Sample Environment 60 3.3.6 D22 Data Reduction 61 3.4 Nuclear Magnetic Resonance Sample Environment 63 Chapter 4 Simulation Theory 65 4.1 Introduction 65 4.2 Metropolis Monte Carlo 67 4.3 Interatomic Potentials 69 4.4 Boundary Conditions and Cut-off Rules 71 4.5 Empirical Potential Structural Refinement 73 4.5.1 The EPSR Procedure 73 4.5.2 The Spatial Density Function 77 Chapter 5 Results I: Neutron Scattering 79 5.1 Introduction 79 5.2 Wide Angle Diffraction Studies of Metal-Ammonia-Fulleride Solutions 80 5.2.1 Introduction 80 5.2.2 Experimental Details 81 5.2.3 Total Structure Factors and Pair Distribution Functions 82 5.2.4 Results and Discussion I 86 5.2.5 EPSR Analysis 89 5.2.5.1 Simulation Details 89 5.2.6 Results and Discussion II, EPSR 90 5.2.6.1 Solvent-Solvent Structure 96 5.2.6.2 Fulleride Solvation Structure 99 5.2.6.3 Potassium Solvation 105 5.2 6.4 Anion-Cation Correlations 107 5.2.6.5 Inter-fulleride Structure 108 5.2.7 Conclusions 108 5.3 Small Angle Neutron Scattering Studies (SANS) of Metal-Ammonia- Fulleride Solutions 109 5.3.1 Calculations o f SANS Patterns 109 5.3.2 Experimental 113 5.3.3 Results 114 5.3.4 Conclusions 116 Chapter 6 Results II: Computer Simulations 118 6.1 Introduction 118 6.2 Simulation Details 119 6.2.1 Interatomic Potentials 119 6.2.2 Boundary Conditions and Simulation Cells 121 6.2.3 Physical Parameters and Cut-offs 121 6.2.4 General Method 122 6.3 Simulation Analysis 123 6.3.1 Pair Distribution Functions 123 6.3.2 Enthalpy o f Dissolution 124 6.4 Results and Discussion I: Potassium-Fulleride-Ammonia Solution, K5C6o(NH3)250 126 6.4.1 Enthalpy o f Dissolution 130 6.5 Results II: The Effect of Fulleride Charge, Simulations