Assessment of the performance of commonly used DFT functionals vs. MP2 in the study of IL-Water, IL-Ethanol and IL-(H2O)3 clusters

We present a comparative study of the accuracy of different DFT approaches vs. MP2 for evaluating ionic liquids (ILs) + cosolvent. Namely, we are interested in [XBmim] + cosolvent (X being Cl−, BF4−, PF6−, and CH3SO3− anions and cosolvent being water or ethanol) and [XBmim] + (H2O)3 clusters. In this study the B3LYP, B3LYP-D3, M06, M06-2X and M06-HF functionals with Pople and Dunning basis sets are considered. We find that the influence of the basis sets is a factor to take into consideration. As already seen for weakly bonded systems when the basis set quality is low the uncorrected counterpoise (unCP) or averaging counterpoise (averCP) energies must be used due to cancellation errors. Besides, the inclusion of extra diffuse functions and polarization is also required specially in the case of ILs interacting with water clusters. The B3LYP functional does not reproduce either the structure or the interaction energies for ILs + H2O and ILs + EtOH aggregates, the energetic discrepancies being more significant than the structural ones. Among the dispersive corrected functionals, M06-2X results resemble to a great extent the reference data when the unCP interaction energies are considered for both water and ethanol. In turn, M06 and B3LYP-D3 functionals are the best option for ILs containing polar and non-polar anions, respectively, whether the averCP interactions energies are taking into consideration. From the structural point of view, B3LYP and M06 functionals describe more open structures whereas B3LYP-D3, M06-2X and M06-HF structures resemble quite well MP2 results. When the number of water molecules increases the H bonding motif gains importance and the effect depends on the underlying functional. Only M06-2X and M06-HF behaviour is similar to that observed for one water molecule. This is important because to describe ILs-cosolvent solutions is not only necessary to take into account the ILs-cosolvent interactions but also the cosolvent-cosolvent ones in the ensemble of the system.Junta de Andalucía FQM282Ministerio de Ciencia e Innovación CTQ2011-2593

Computational investigation of ionic liquids

Ionic liquids have been extensively studied over the past few decades to take advantage of their fine-tunable physicochemical properties. Due to the high cost of synthesis as well as a large number of ion combinations, it is beneficial to investigate them using computational chemistry methods. At the same time, it is also challenging to find a suitable computational approach that captures the whole variety of different types of interactions present in ionic liquids. In this work, we have compared the performance of PBE, M06-L, SCAN, SCAN0, and B2PLYP density functionals when describing ionic liquids. DLPNO-CCSD(T) method extrapolated to the complete basis set limit is used as a reference. In addition,we have constructed a density functional theory-based model to evaluate the electrochemical stability and viscosity of ionic liquids. This simple yet efficient model correlates the macroscopic properties to our computational results

Soluut-solvent vastasmõjude eksperimentaalne uurimine ja modelleerimine

Väitekirja elektrooniline versioon ei sisalda publikatsiooneEnamik praktilist tähtsust omavatest keemilistest protsessidest toimub vedelikes – mitte ainult tööstuslik süntees ja laborikeemia, vaid ka bioloogilised protsessid nagu rakkude hingamine toimuvad molekulaarsel tasemel keerulise koostisega lahustes. Neist protsessidest arusaamine ja molekulide käitumise ennustamine lahustes on tähtis arvukate uurimisvaldkondade jaoks, meditsiinist ja farmakoloogiast naftakeemiani. Kahjuks on ainete omaduste ennustamine vedelikes arvutuskeemia jaoks üks keerulisemaid ülesandeid. Käesolevas töös hinnati olemasolevate arvutusmetoodikate sobivust vesiniksideme tekke kirjeldamiseks orgaanilistes lahustites ning molekulide jaotuse kirjeldamiseks kahe vedeliku vahel (sisuliselt vedelik-vedelik ekstraktsiooni modelleerimiseks). Peamine kasutatud arvutusmeetod oli COSMO-RS (Conductor-like Screening Model for Real Solvents), valitud oma erakordse sobivuse tõttu kontsentreeritud ja mitmekomponendiliste lahuste omaduste ennustamiseks ja molekulaardisainiks. Töö käigus leiti, et vesiniksidemed neutraalsete molekulide vahel on kirjeldatavad suhteliselt hästi, kuid vaadeldud arvutusmetoodikad pole piisavalt täpsed negatiivselt laetud vesiniksidemega komplekside modelleerimiseks. Vedelik-vedelik ekstraktsiooni tulemuste ennustamine COSMO-RS meetodiga oli üldjuhul edukas. Saadud tulemustele (nii lõpp- kui vahepealsetele parameetritele) saadi täpsuse hinanngud. Peale selle arendati uus metodoloogia tundmatute ühendite jaotuse ennustamiseks kahe mitteseguneva vedeliku vahel ilma vajaduseta ühendeid identifitseerida. See lihtsustab parima lahusti valikut ainete isoleerimiseks või puhastamiseks, vähendades töö- ja kemikaalide kulu ning jäätmete kogust.The majority of practically relevant chemical processes occur in liquids. Those are not limited to industrial synthesis and laboratory chemistry – biological processes such as cellular respiration on molecular level take place in complex solutions. Understanding and being able to predict the behaviour of molecules in solutions is essential for numerous branches of science, ranging from medicine and pharmacology to petroleum chemistry. However, predicting the behavior of chemical compounds in liquids, especially in many-component solutions, is one of the most challenging tasks for computational chemistry. In this work existing computational methodologies were tested for suitability for describing hydrogen bond formation in organic solvents and distribution of organic compounds between liquids (essentially modeling of liquid-liquid extraction). The main computational method in this work is COSMO-RS (Conductor-like Screening Model for Real Solvents), chosen for its unequalled ability to predict properties of concentrated and multicomponent solutions and usability in molecular design. It was found that properties of hydrogen bonds between uncharged molecules can be predicted relatively well, but the tested computational approaches were not accurate enough for description of hydrogen bonds involving negatively charged ions. Modeling of liquid-liquid extraction using COSMO-RS was generally successful. Accuracy of the predictions and intermediate parameters was evaluated and problematic cases identified and discussed. Also, a new methodology was developed for predicting the distribution of unknown compounds between immiscible solutions without need for compound identification. It allows simplifying the solvent selection for compound isolation or purification, reducing the workload, expenses and waste amount

Computational approaches to understanding reaction outcomes of organic processes in ionic liquids

This review considers how various computational methods have been applied to explain the changes in reaction outcome on moving from a molecular to an ionic liquid solvent. Initially, different conceptual approaches to modelling ionic liquids are discussed, followed by a consideration of the limitations and constraints of these approaches. A series of case studies demonstrating the utility of computational approaches to explain processes in ionic liquids are considered; some of these address the solubility of species in ionic liquids while others examine classes of reaction where the outcome in ionic liquids can be explained through the application of computational approaches. Overall, the utility of computational methods to explain, and potentially predict, the effect of ionic liquids on reaction outcome is demonstrated

Structural and Thermodynamic Properties of Transition Metal Ions in Room Temperature Ionic Liquids

openRoom temperature ionic liquids (RTILs) are salts made by an organic cation and an organic or inorganic anion, which are at the liquid state at 25 °C. RTILs have attracted much attention as new sustainable solvents owing to some unique properties they usually possess, such as a practically negligible vapor pressure, non-flammability, high thermal stability, wide electrochemical windows, good solvation ability and supposed low toxicity. These features make RTILs good candidates for the substitution of classical organic solvents in many technological applications. For these reasons, they are currently studied as new media for chemical separations, electrodepositions, electrolytes for batteries and supercapacitors, catalysis and pharmaceutical research. Several of these applications also involve the presence of metal ions as solvated species in RTILs. In this field, structural and thermodynamic data about single-ion solvation are fundamental quantities that need to be known to improve new technologies. However, this fundamental knowledge still lacks for many metal species in several ionic liquids. The aim of this thesis is to obtain a complete description of metal ions solvation in RTILs both from a structural and thermodynamic point of view. Molecular dynamics (MD) simulations and X-ray absorption spectroscopy (XAS) experiments have been performed to study solutions of metal ions of industrial, environmental and economic interest such as Zn2+, Co2+, Ag+ in widely used RTILs like those based on the [Tf2N]- (bis(trifluoromethylsulfonyl)imide) and [BF4]- (tetrafluoroborate) anions within the [Cnmim]+ (1-alkyl-3-methylimidazolium) cation. MD simulations have been carried out on Zn2+ in [Cnmim][Tf2N] (n = 2, 4) and [C4mim][BF4]. The obtained thermodynamic data are in good agreement with literature experimental values and indicate the goodness of the employed protocol. The calculated Gibbs free energies of transfer (ΔGtrans) from water to the [Cnmim][Tf2N] RTILs suggest that Zn2+ is more favorably solvated in aqueous solution than in this class of ionic liquids, while the opposite is found for [C4mim][BF4]. The obtained single-ion solvation enthalpies and entropies provided an interpretation of the different contributions to the calculated free energies. In addition, XAS experimental results allowed to understand the coordination of Zn2+ in water-saturated [C4mim][Tf2N], representing the real-operating condition in a liquid-liquid extraction. A similar picture has been obtained for Co2+ in [C4mim][Tf2N]. MD calculated ΔGtrans showed that the metal ion is still more favorably solvated in water than in the RTIL because of an unfavorable entropic contribution. XAS experiments and data-fitting allowed to obtain Co2+ coordination in dry [C4mim][Tf2N]. The metal resulted to be bound by six monodentate anions forming the [Co(Tf2N)6]4- octahedral species. In addition, water is found to preferentially coordinate the metal when present at high concentrations in the RTIL, as provided by UV-Vis data. As regards the study about Ag+ in RTILs, a totally different picture with respect to Zn2+ and Co2+ has been obtained. MD results showed that this ion is more favorably solvated both in [C4mim][Tf2N] and [C4mim][BF4] with respect to water, and this encourages the employment of these RTILs as extracting phase for this metal. Ag+ resulted coordinated by four or five RTILs anions, depending on the employed interaction potential. However, when considering the transfer of Ag+ from water to the RTILs, great care must be taken because of a possible change in the coordination number. Indeed, preliminary XAS data suggest a linear coordination for this metal ion in aqueous solution, differently from the tetrahedral model that is usually accepted and reproduced by the current classical potentials. Ab initio MD simulations with the Car-Parrinello method seemed to confirm this observation.Dottorato di ricerca in Scienze dell'ingegneria energetica e ambientaleopenBusato, Matte

Synthesis of protic ionic liquids. Challenges and solutions for the synthesis of pure compounds.

The urgent need to diversify our energy matrix is responsible for a renewed interest in fuel cell technology, which can use hydrogen gas, a renewable green fuel, as an energy source. This technology is currently a commercially available option, however, it still requires technological improvements before it can be widely\ua0used for different applications. One way this technology could potentially be improved is by increasing its temperature range of operation by developing new, anhydrous proton conducting materials. Protic ionic liquids, which are organic salts with low melting temperatures, are interesting candidates for this application, since they can conduct protons in the operational conditions of fuel cells and without the need of water. These compounds can be synthesized by a simple\ua0acid-base neutralization reaction, but certain considerations must be taken in\ua0order to obtain high quality (dry and pure) protic ionic liquids. In this thesis, a series of triazolium and imidazolium based protic ionic liquids were synthesized\ua0using a solvent-free method designed to address several limitations encountered\ua0with other commonly used methods. Using this method, pure (98-99% m/m) and dry (128-553 ppm of water) protic ionic liquids were synthesized (in a laboratory scale) without the need for purification methods that require heating the\ua0ionic liquid, hence avoiding the common issue of thermal decomposition. This method was also designed to allow for the accurate measurement of acid and\ua0base, and for the controlled mixing of both compounds, which is essential to\ua0avoid producing impure protic ionic liquids with excess of either acid or base. The system is consists of only glass and chemically resistant polymer(PTFE and PVDF) parts, which avoids other contaminants that can result from unwanted\ua0reactions involving the reagents with common laboratory tools (metallic objects, paper, plastic, etc.). The resulting ionic liquids were carefully analyzed by spectroscopic and thermal analysis methods designed to avoid water absorption, which is known to affect their properties. To complement this experimental characterization, computational chemistry tools were used to assess the ionic liquids’ properties, as well as to assign vibrational modes

Metalli–vesilahuse ja metalli–ioonse vedeliku elektrilise kakskkihi arvutuslik uurimine

Väitekirja elektrooniline versioon ei sisalda publikatsiooneKäesolevas teadustöös uurisime metalli ja vesilahuse ning metalli ja ioonse vedeliku vahelist elektrilist kaksikkihti, keskendudes pindkihi dipoolse struktuuri analüüsile. Hindasime selle komponente elektrilise kaksikkihi kompaktses osas, mis jääb Helmholtzi välise kihi ja metalli pindkihi vahele. Alustasime pindkihi struktuuri ning elektrilise kaksikkihi diferentsiaalmahtuvuse arvutusliku uuringuga vismuti, galliumi ja elavhõbeda pinnal vesilahustes. Saadud tulemused kinnitavad molekulide adsorptsiooni olulist rolli elektrilise kaksikkihi omaduste kujunemisel. Seejärel kogusime arvutuslikke andmeid metalli ja ioonse vedeliku pindkihi struktuuri kohta, ning uurisime kuidas see määrab pindkihi dipoolse ehituse ning diferentsiaalmahtuvuse. Kasutasime ioonse kaksikkihi mudelit, mis sobib nii vastasioonide adsorptsiooni tõttu tekkinud dipooli kui ka anioonide ja katioonide vastastikuste mõjutuste tõttu tekkinud dipooli kirjeldamiseks. Süsiniku pinnal paiknevat ioonpaari käsitlevas uuringus näitasime, et kovalentne side vähendab oluliselt dipoolmomenti väärtust ning potentsiaalilangust elektroodi–elektrolüüdi pindkihis, mille tulemusena suureneb elektrimahtuvus. EMImBF4 ioonassotsiaatide võrdlemisel kulla, vismuti ja süsiniku pinnal selgus, et elektrolüüdikihi dipool mõjutab oluliselt mahtuvuse elektroodi potentsiaalist sõltuvuse kõvera kuju. Põhimõtteline erinevus vesilahuse ja ioonse vedeliku elektrilise kaksikkihi omaduste vahel tuleneb nende molekulaarse ja ioonse struktuuri erinevusest. Esitatud andmed annavad kasulikku teavet vesilahuse ja ioonvedeliku adsorptsiooni kohta erinevatel metallidel. Teave nende tegurite vastastikuste mõjude kohta võib aidata leida seoseid metalli ja elektrolüüdi pindkihi struktuuri ning pindkihtide toimimise vahel energia muundamise ja salvestamise seadmetes.In this thesis, we investigated the electrical double layer at metal–aqueous solution and metal–ionic liquid interfaces. For both aqueous and ionic liquid interfaces, we focused on the characteristics of interfacial dipole created at metal–electrolyte interface. We analysed its components on the example of the compact layer – the region between the outer Helmholtz plane and the interface. We started with a computational investigation of interfacial structure and differential capacitance of the electrical double layer at Bi, Ga, and Hg electrodes in aqueous electrolyte solution. The obtained results stress the significant role of the interfacial water layer in the interfacial properties of a metal surface–electrolyte solution interface. Then we gained computational insights into the structure of the metal–ionic liquid interfaces and how it determines the interfacial dipole as well as the differential capacitance. We introduced an ionic bilayer model that accounts for the dipole formed due to the adsorption of counter-ions as well as for the dipole formed due to anion–cation interplay. In a study of an ionic pair at circumcoronene surface, we showed that the covalent bonding significantly reduces the interfacial dipole moment value as well as the potential drop at an electrode–electrolyte interface, thus, leading to the capacitance increase. Comparison of the behaviour of EMImBF4 ionic associates at gold, bismuth and circumcoronene surfaces revealed that electrolyte layer dipole composition and structure play a crucial role in determining the shape of the capacitance vs. electrode potential curve. The conceptual difference between the properties of the aquoues and ionic liquid electrical double layers is dictated by the difference in their molucular and ionic structures. The reported data provide useful information on the water and ionic liquid adsorption on the metal surfaces. The enlighten interaction mechanisms may help to find links between the interfacial structure of the metal–electrolyte interfaces and their performance in energy conversion and storage devices

How Voltage Drops are Manifested by Lithium Ion Configurations at Interfaces and in Thin Films on Battery Electrodes

Battery electrode surfaces are generally coated with electronically insulating solid films of thickness 1-50 nm. Both electrons and Li+ can move at the electrode-surface film interface in response to the voltage, which adds complexity to the "electric double layer" (EDL). We apply Density Functional Theory (DFT) to investigate how the applied voltage is manifested as changes in the EDL at atomic lengthscales, including charge separation and interfacial dipole moments. Illustrating examples include Li(3)PO(4), Li(2)CO(3), and Li(x)Mn(2)O(4) thin-films on Au(111) surfaces under ultrahigh vacuum conditions. Adsorbed organic solvent molecules can strongly reduce voltages predicted in vacuum. We propose that manipulating surface dipoles, seldom discussed in battery studies, may be a viable strategy to improve electrode passivation. We also distinguish the computed potential governing electrons, which is the actual or instantaneous voltage, and the "lithium cohesive energy" based voltage governing Li content widely reported in DFT calculations, which is a slower-responding self-consistency criterion at interfaces. This distinction is critical for a comprehensive description of electrochemical activities on electrode surfaces, including Li+ insertion dynamics, parasitic electrolyte decomposition, and electrodeposition at overpotentials.Comment: 35 pages. 10 figure

Principles of Chemical Reactivity on the Diels-Alder Reaction in Ionic Liquids and Lewis Acid Catalysis using Large-Scale Computations

My Ph.D. dissertation describes three different external influences on pericyclic reactions: (1) ionic liquids, (2) Lewis acids and (3) bis(oxazoline)-Cu(II) complexes. (1) Ionic liquids deliver enhanced rates and endo/exo selectivities on the Diels-Alder reaction. The goal is to establish a firm understanding of the molecular interactions that give rise to the observed rate and selectivity enhancements. In order to accomplish our goal, we have used density functional theory methodology, specifically the Becke three parameter with Lee, Yang and Parr corrections at the 6-31G(d), to describe short-range effects, and have created new force field parameters using CHARMM to allow faster classical computations and explore bulk phase effects. (2) Lewis acids are known to influence strongly the rate, regio, endo/exo, diastereofacial and enantio selectivities of the Diels-Alder reaction. Specifically, asymmetric catalysis using chiral Lewis acids provides a crucial tool in the enantioselective synthesis of chiral organic compounds. Uncovering the differential forces between the ground and transition structures with chiral Lewis acids is a perquisite step towards the creation of more effective enantioselective catalysts. Our efforts focus upon a novel combination of two specific intermolecular interactions between boron Lewis acids and Diels-Alder transition structures. Quantum mechanical calculations along with kinetic isotope effects are used in conjunction to elucidate these specific interactions. (3) Cu(II) functions effectively as a Lewis acidic center that has proven to control the stereoselectivity of a wide range of organic reactions. Specifically, bis(oxazoline) copper(II) complexes operate as enantioselective Lewis acid catalysts for carbocyclic and hetero Diels-Alder reactions. We have used quantum mechanical calculations in order to determine how ligand field strength influences Cu(II) coordination and ultimately the stereoselectivity of organic reactions

The nature of interactions in Alkylimidazolium based ionic liquids

Ionic liquids are materials that have the ability to be designed for specific tasks. Their properties can be adjusted by changing the molecular constituents of the liquid or the intermolecular interactions between composite ions through functionalisation. Therefore, understanding the nature of the interactions between ions is important. In the thesis, we use density functional theory calculations to obtain conformers of 1-ethyl-3-methylimidazolium ([emim]+)paired with the anions [Cl]-, [Br]-, [MeCO2]-, [CF3CO2]-, [MeSO3]-, [CF3SO3]-, [BF4]- and [PF6]-. We analyse the structures of the pairs and then explore the nature of the electrostatic, dispersion and hydrogen bonding interactions. Electrostatic interactions were the most dominant interactions. The dispersion interaction energies were found to be of the same order as the estimated energy of the hydrogen bond. The non-covalent index (NCI) analysis was used to visualise the non-covalent interactions in real space as enclosed surfaces. The properties of the surfaces were used to characterise interaction types, namely van der Waals interactions and hydrogen bonds. Furthermore, we find that the density enclosed within the hydrogen bonding surfaces can be used to estimate the potential of the hydrogen bond. To our knowledge, a potential for hydrogen bonding from NCI has not been explored for ionic liquids. Finally, the average strength of the hydrogen bond was calculated from structures extracted from molecular dynamics simulations. They reveal that the hydrogen bond strength for [emim][MeCO2] is approximately two-thirds weaker in the condensed phase than in the gas phase. The effect of the polarising environment is also found to weaken the hydrogen bond slightly