Noble Gas Chemistry

Noble Gas Chemistry Noble Gas Chemistry Structure, Bonding, and Gas-Phase Chemistry Felice Grandinetti Author All books published by Wiley-VCH are carefully produced. Nevertheless, authors, Prof. Felice Grandinetti editors, and publisher do not warrant the Dipartimento per la Innovazione nei information contained in these books, sistemi Biologici including this book, to be free of errors. Agroalimentari e Forestali (DIBAF) Readers are advised to keep in mind that Università della Tuscia, L.go statements, data, illustrations, procedural dell’Università details or other items may inadvertently s.n.c., 01100 Viterbo be inaccurate. Italy Library of Congress Card No.: applied for and British Library Cataloguing-in-Publication Data Istituto per le Metodologie Chimiche del A catalogue record for this book is CNR available from the British Library. Via Salaria, Km 29.500 00015 Monterotondo, RM Bibliographic information published by Italy the Deutsche Nationalbibliothek The Deutsche Nationalbibliothek lists Cover: © Rvo233/iStockphoto this publication in the Deutsche Nation- albibliografie; detailed bibliographic dataareavailableontheInternetat <http://dnb.d-nb.de>. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Boschstr. 12, 69469 Weinheim, Germany All rights reserved (including those of translation into other languages). No part of this book may be reproduced in any form – by photoprinting, microfilm, or any other means – nor transmitted or translated into a machine language with- out written permission from the publish- ers. Registered names, trademarks, etc. usedinthisbook,evenwhennotspecif- ically marked as such, are not to be con- sidered unprotected by law. Print ISBN: 978-3-527-34180-1 ePDF ISBN: 978-3-527-80352-1 ePub ISBN: 978-3-527-80354-5 oBook ISBN: 978-3-527-80355-2 Typesetting SPi Global, Chennai, India Printing and Binding Printed on acid-free paper 10987654321 v Contents Preface ix Part I An Overview of Noble Gas Chemistry 1 1 A Historical Introduction 3 1.1 The Discovery of the Elements 3 1.2 The Emerging of Different Chemistries 7 1.2.1 Bulk-Phase Compounds 8 1.2.2 Molecules in Cold Matrices 11 1.2.3 Molecules in Liquid and Supercritical Noble Gases 12 1.2.4 Chemistry Under High Pressures 13 1.2.5 Gaseous Neutral Complexes 14 1.2.6 Gas-Phase Ion Chemistry 16 1.3 The Development of the Diverse Fields 18 2 Typical Compounds and Bonding Motifs 23 2.1 General Considerations 23 2.2 Clusters of Noble Gas Atoms 26 2.3 Monocoordinated Compounds 29 2.4 Dicoordinated (‘Inserted’) Compounds 30 2.5 Polycoordinated Compounds 41 2.6 Cage, Inclusion, and Adsorption Compounds 47 2.7 The Effects of the Pressure 51 3 Chemistry in Silico 55 3.1 TheRoleofCalculationsinNobleGasChemistry 55 3.2 Methods of Bonding Analysis 56 3.2.1 The AIM Theory 56 3.2.2 The Analysis of the ELF 57 3.2.3 The Analysis of the H(r) 58 3.2.4 The NBO Analysis 62 3.2.5 The EDA-NOCV Analysis 64 3.2.6 The Analysis of the CD Function 66 vi Contents 3.3 About the Performance of the Theoretical Methods 66 3.4 Illustrative Examples 70 3.4.1 Probing the Bonding Character 70 3.4.2 Structure and Stability of the XeFn (n = 1 − 6) 84 3.4.3 Open-shell Compounds 88 3.4.4 Exploring the PES 91 3.4.5 Neutral Compounds of Helium and Neon 99 3.4.6 Novel Compounds of Argon, Krypton, and Xenon 123 3.4.7 Radon Compounds 133 3.4.8 The Aerogen Bond 138 Part II Gas-Phase Chemistry of the Noble Gases 147 4 Neutral Species 149 4.1 Complexes with Atoms and Diatomic Molecules 149 4.1.1 The Interaction Energy 149 4.1.2 The Correlation Formulas 150 ′ 4.1.3 The Ng2 and NgNg 154 4.1.4 About the van der Waals Radii of the Noble Gases 157 4.1.5 The Efimov State of3 He 159 4.1.6 Complexes with H2,N2,andO2 160 4.1.7 Complexes with C2,CO,andCS 162 4.1.8 Complexes with the Dihalogens 166 4.1.9 Complexes with the Hydrogen Halides 173 4.1.10 Complexes with Diatomic Metal Halides 178 4.2 Complexes with Polyatomic Molecules 183 4.2.1 Complexes with CO2,CS2,andCOS 183 4.2.2 Complexes with H2OandNH3 186 4.2.3 Complexes with Hydrocarbons 191 4.2.4 Complexes with Halocarbons 194 4.2.5 Complexes with Other Organic Molecules 197 4.3 Dicoordinated Covalent Compounds 200 5 Ionic Species 203 5.1 Noble Gases as Ligands of Ionic Species 205 5.1.1 Complexes with Metal Cations 205 5.1.2 Complexes with Non-Metal Cations 220 5.1.3 Complexes with Anions 227 5.2 Protonated Noble Gases and Other Related Species 229 5.2.1 ArH+ as a Naturally Occurring Species 229 + + 5.2.2 The NgH and NgmHn 231 5.2.3 Complexes of the NgH+ with Simple Ligands 241 5.2.4 Other Noble Gas Ions of Potential Interstellar Interest 244 5.3 Noble Gas Ionic Reactions 249 5.3.1 Reactions Involving Singly-charged Cations 249 5.3.2 Reactions Involving Doubly-charged Cations 253 Contents vii A Chemical Composition of Air 259 B Ab Initio and DFT Electronic Structure Methods 261 C Atomic Charges of Diatomic Molecules 269 D Bond Distances and Polarisabilities of Diatomic Molecules 271 References 273 Index 337 ix Preface The elements of group 18 (the noble gases) are, generally, perceived as only less reactive. Only krypton and xenon form, in fact, isolable compounds (the radioac- tive and short-lived radon is hardly investigated), and the synthesis of compounds containing helium, neon, and argon still remains an open challenge. Chemistry is, however, also a matter of environment and conditions, and, particularly for noble gas chemistry, a proper choice of these factors may open doors that would remain, otherwise, definitely locked. The HArF detected so far in cold matrices, and the Na2He recently obtained at the highest pressures (unique compounds of argon and helium, respectively), are two major illustrative examples. But the binding capabilities of the noble gases are greatly enhanced also under the isolated conditions of the gas phase. In this environment, all the elements, including helium and neon, really ‘forget’ to be inert, and form an exceptionally large family of molecular species, ranging from fragile van der Waals adducts to strongly bound covalent species. A variety that is, probably, unique in the periodic table! Inter- estingly, this richness is, in essence, the daughter of the inertness. Thus, while resistant (especially He, Ne, and Ar) to definitely break their electronic clouds to form true ionic or covalent bonds, the noble gas atoms are still sensitive to the polarisation effects exerted by neutral and ionic binding partners. The stabilis- ing interactions thus range from dispersion forces to electrostatic and inductive interactions, with in case contribution of charge transfer. And the spectrum of the bonding motifs further enlarges under photodissociating or ionising conditions that favour also the formation of true covalent bonds. The simplest HeH+ was, indeed, first detected in 1925, nearly 40 years before the breakthrough advances in xenon chemistry that officially destroyed the myth of noble gas inertness! And ArH+ was quite recently detected in the galactic and extragalactic regions as the first naturally occurring species containing a noble gas atom: a connection between Nature and laboratory that, certainly, rejuvenates the interest for the gas-phase chemistry of the noble gases. This is, indeed, the main topic of this book, with emphasis on both neutral and ionic species. The matter is, certainly, of experimental interest, but it enjoys also the major contribution of the calculations that are extensively employed not only to aid the interpretation of the experiments but also to independently explore still unreported molecules and ions. The subtitle of the book ‘Structure, Bonding, and Gas-Phase Chemistry’ wishes also to emphasise the strict relationship in this field between experiments and theory. x Preface The book is divided in two parts. The first one (Chapters 1–3) is intended asan introductory overview of noble gas chemistry, also functional to the second part, more specifically concerned with gaseous neutral (Chapter 4) and ionic species (Chapter 5). Chapter 1 is, in particular, a historical introduction to noble gas chemistry, aimed at emphasising the salient facts that marked the discovery of the elements, the emerging of their reactivity under different experimental conditions, and the subsequent evolution of these fields. Chapter 2 illustrates a classifi- cation of noble gas compounds, grouped here in five categories (clusters of noble gas atoms, monocoordinated-, dicoordinated-, polycoordinated compounds, and cage, inclusion, and adsorption compounds) that appeared best suited for gaseous species. Alternative classifications could be, certainly, generally taken, and I could say the same for the selected illustrative examples. Chapter 3 is concerned with the applications of the calculations, with emphasis on issues of major interest in noble gas chemistry, particularly gas-phase chemistry: the structure and stability of noble gas compounds, their bonding character, and the kinetics of their formation and decomposition processes. The methods most extensively employed to perform the bonding analysis of noble gas compounds are also shortly recognised here. The methods most commonly employed for electronic structure calculations were, instead, briefly recalled in Appendix B. Chapter 4 is, mainly, concerned with the structure, bonding, and stability of gaseous neutral species. The first discussed systems are monocoordinated adducts of diverse composition and complexity, examined in terms of a preliminarily outlined inter- pretative model. Gaseous dicoordinated covalent compounds are also accounted. Chapter 5 is concerned with gas-phase ion chemistry, and illustrates issues of current interest such as the behaviour of the noble gases as ligands of ionic species, the chemistry of protonated noble gases and other related species, and the properties of other ions of potential interstellar interest.

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