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Analysis of Chemical Bonding and Aromaticity from Electronic Delocalization Descriptors

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Analysis of Chemical Bonding and Aromaticity from Electronic Delocalization Descriptors ANALYSIS OF CHEMICAL BONDING AND AROMATICITY FROM ELECTRONIC DELOCALIZATION DESCRIPTORS Ferran FEIXAS GERONÈS Dipòsit legal: GI-1023-2011 http://hdl.handle.net/10803/37471 ADVERTIMENT. La consulta d’aquesta tesi queda condicionada a l’acceptació de les següents condicions d'ús: La difusió d’aquesta tesi per mitjà del servei TDX ha estat autoritzada pels titulars dels drets de propietat intel·lectual únicament per a usos privats emmarcats en activitats d’investigació i docència. No s’autoritza la seva reproducció amb finalitats de lucre ni la seva difusió i posada a disposició des d’un lloc aliè al servei TDX. No s’autoritza la presentació del seu contingut en una finestra o marc aliè a TDX (framing). Aquesta reserva de drets afecta tant al resum de presentació de la tesi com als seus continguts. En la utilització o cita de parts de la tesi és obligat indicar el nom de la persona autora. ADVERTENCIA. La consulta de esta tesis queda condicionada a la aceptación de las siguientes condiciones de uso: La difusión de esta tesis por medio del servicio TDR ha sido autorizada por los titulares de los derechos de propiedad intelectual únicamente para usos privados enmarcados en actividades de investigación y docencia. No se autoriza su reproducción con finalidades de lucro ni su difusión y puesta a disposición desde un sitio ajeno al servicio TDR. No se autoriza la presentación de su contenido en una ventana o marco ajeno a TDR (framing). Esta reserva de derechos afecta tanto al resumen de presentación de la tesis como a sus contenidos. En la utilización o cita de partes de la tesis es obligado indicar el nombre de la persona autora. WARNING. On having consulted this thesis you’re accepting the following use conditions: Spreading this thesis by the TDX service has been authorized by the titular of the intellectual property rights only for private uses placed in investigation and teaching activities. Reproduction with lucrative aims is not authorized neither its spreading and availability from a site foreign to the TDX service. Introducing its content in a window or frame foreign to the TDX service is not authorized (framing). This rights affect to the presentation summary of the thesis as well as to its contents. In the using or citation of parts of the thesis it’s obliged to indicate the name of the author. PhD thesis: Analysis of Chemical Bonding and Aromaticity from Electronic Delocalization Descriptors Ferran Feixas Geron`es 2010 Doctorat Interuniversitari en $"%ımica 'e`orica i Computacional PhD supervisors: Prof. Miquel Sol`ai Puig Dr. Jordi Poater i 'eixidor Dr. Eduard Matito i Gras Mem`oriapresentada per a optar al t%ıtol de Doctor per la Universitat de Girona El professor Miquel Sol`a i Puig, catedr`aticd’Uni#ersitat a l’`area de $"%ımica F%ısica de la Universitat de Girona. el doctor Jordi Poater i 'eixidor, in#estigador Ram´ony Cajal a l’Institut de $"%&mica Computacional de la Universitat de Girona. i el doctor Eduard Matito i Gras, in#estigador postdoctoral Marie-Curie de l’Institut de F%ısica de la University of Sczczecin. CER'!FIQUEM: Que aquest treball titulat ”Analysis of Chemical Bonding and Aromaticity from Electronic Delocalization Descriptors”, que presenta en Ferran Feixas Geron`es per a l’obtenci´odel t%ıtolde Doctor, ha estat realitzat sota la nostra direcci´oi *ue compleix els re*ueriments per a poder optar a )enci´oE"ropea( Signatura Prof. Miquel Sol`aPuig Dr. Jordi Poater i 'eixidor Dr. Eduard Matito i Gras Girona. de desembre de 2010 ”I quan penses dur a terme el teu somni? -va demanar el mestre al deixeble. Quan tingui la oportunitat -va respondre. El Mestre li contest`a -L’oportunitat mai no arriba. L’oportunitat ´esaqu´ı.” !nthony de Mello ! tots vosaltres # Preface Since the advent of quantum mechanics. theoretical and computational chemistry ha#e played a pivotal role in chemistry( From the #ery 3eginning, theoretical chemists ha#e 3een primarily focused on the development of new methodologies that may provide an explanation for most of the chemical phenomena( Ho5ever, progress in the applica3ility of theoretical and computational chemistry depends on the advances in computational po5er. This fact limited the interaction 3et5een ex- perimental and theoretical chemists for a long time. Notwithstanding. at the end of the first decade of the 2 st century. 5e ha#e arrived at a position where theory and experiment play a complementary role in exploring chemical questions. Theoretical chemistry is no5 commonly used to address complex problems in chemistry. bio2 chemistry. or materials science. from the study of small molecules in the gas phase to the simulation of protein folding in complex environments.1 Interactions 3et5een electrons determine the structure and properties of matter from molecules to solids( Therefore. the understanding of the electronic structure of molecules will enable us to extract relevant chemical information. Since the 5ork of Lewis,2 the concept of electron pair has 3een placed at the epicenter of the discussion about the properties of chemical 3onding. Hence, the pair density. that accounts for the correlated motion of a couple of electrons, has 3een #ery important in the interpretation of electronic structure. 'he pair density and its related quantities. such as the concept of Fermi Hole, are discussed in detail in Chapter ( !nterestingly. these *uantities ha#e 3een 5idely used to elucidate the nature of chemical 3onding in a plethora of systems( In chemistry. global molecular properties are as important as the properties of a given atom or region of the molecular space. 'he partition of molecular space into different regions helps "s to unra#el ho5 the electrons are localized in a specific region or which is the num3er of electrons shared among t5o or more regions of the space. In Chapter 2 5e 5ill see ho5 5e can more clearly un- derstand the nature of chemical 3onding from the concept of electron delocalization. From the disco#ery of 3enzene in <253 to the present day. the concept of aro2 maticity has experienced se#eral revolutions that ha#e fueled the interest of 3oth theoretical and experimental chemists( The disco#ery of new aromatic compounds is not a3out to slo5 do5n. Undoubtedly. the major breakthrough of the last decade in the field of aromaticity took place in 2001, when the first all-metal cluster, MAl4− >) ? Li, Na. or Cu), 5as characterized.4 This finding ga#e rise to one of the most vii striking features of all-metal aromatic clusters, the so2called multifold aromaticity. that is. the presence ofσ2.π2.δ2. or evenφ-aromaticity( As the num 3er of new aro- matic molecules grows, the quest for the quantification of aromaticity has 3ecome one of the challenges of theoretical chemists. 'hus, the concept of aromaticity is one of the cornerstones of past and current chemistry( Ho5ever, at the same time, it is also considered a chemical unicorn 5 due to the fact that aromaticity is not a directly measurable property. and it cannot 3e defined unambig"ously( In Chapter A. the main advances in the field and the most widely used descriptors of aromaticity 5ill 3e reviewed. On the other hand, Chapters =. C. and D are devoted to the applications of the abo#e presented theory and correspond to the 5orks of the present thesis, that con2 tains t5elve accepted publications. First, 5e focus our attention on the analysis of chemical 3onding 3y means of the Electron Localization Function >ELF)6 and the Domain-A#eraged Fermi Hole analysis (DAFH)(7,8 The four projects collected in Chapter = are a consequence of the research stays at the Universit%ePierre et Marie-Curie with Prof. Bernard Silvi, and at the Czech Academy of Science with Prof. Ro3ert Ponec( In the first section, the E:F is approximated in terms of natu- ral orbitals in order to 3ridge the gap 3et5een the (expensive@ correlated expression and the (sometimes inaccurate) monodeterminantal definition. The next sections are dedicated to DAFH analysis( First, this analysis is generalized to open-shell systemsE second, the open-shell definition is used to analyze the 3onding patterns of some triplet dications; and, third, the peculiarities of the ultrashort Cr-Cr 3ond are analyzed from the point of view of DAF6( In recent years, many methods to quantify aromaticity based on different physico- chemical properties ha#e 3een proposed. !n Chapter C 5e assess the performance of these indicators 3y analyzing their advantages and drawbacks. Throughout this chapter, 5e propose a series of tests based on 5ell-known aromaticity trends that can 3e applied to evaluate the aromaticity of current and future indicators of aromatic- ity in 3oth organic and inorganic species. Since the aromaticity is tightly connected with the concept of electron delocalization, in Chapter D 5e in#estigate the nature of electron delocalization in 3oth aromatic and antiaromatic systems in the light of 6Fuc9el’s >Gn H 2@ rule. Finally. from the conclusions gathered in Chapter C. 5e analyze the phenomenon of multiple aromaticity in all-metal clusters that present σ.π. and/orδ aromaticity( viii Resum de la tesi Des del sorgiment de la mec`anicaqu`antica, la *"%ımicate`oricai computacional ha jugat un paper fonamental en el m´on de la *"%ımica. Des de 3on principi. els *"%ımics te`orics s’han centrat en el desen#olupament de no#es metodologies que poden propor2 cionar una explicaci´oper a la majoria de fen´omens *"%ımics.No obstant, els a#en¸cos en l’aplicaci´ode la *"%ımica computacional han estat molt lligats als a#en¸cos en el camp de la computaci´o. Aquest fet ha limitat la interacci´oentre els *"%ımics exper2 imentals i te`orics durant gran part del segle KK( 'ot i aix`o.
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