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Mosely JJ, Tschumper GS. Probing the Effects of Size and Charge on the Monohydration and Dihydration of SiF 5- and SiF 62- via Comparisons with BF 4- and PF 6. J Phys Chem A 2024. [PMID: 38976798 DOI: 10.1021/acs.jpca.4c03430] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/10/2024]
Abstract
This study systematically examines the interactions of the trigonal bipyramidal silicon pentafluoride and octahedral silicon hexafluoride anions with either one or two water molecules, (SiF5-(H2O)n and SiF62-(H2O)n, respectively, where n = 1, 2). Full geometry optimizations and subsequent harmonic vibrational frequency computations are performed using the CCSD(T) ab initio method with a triple-ζ correlation consistent basis set augmented with diffuse functions on all non-hydrogen atoms (cc-pVTZ for H and aug-cc-pVTZ for Si, O, and F; denoted as haTZ). Two monohydrate and six dihydrate minima have been identified for the SiF5-(H2O)n systems, whereas one monohydrate and five dihydrate minima have been identified for the SiF62-(H2O)n systems. Both monohydrated anions have a minimum in which the water molecule adopts a symmetric double ionic hydrogen bond (DIHB) motif with C2v symmetry. However, a second unique monohydrate minimum has been identified for SiF5- in which the water molecule adopts an asymmetric DIHB motif along the edge of the trigonal bipyramidal anion between one axial and one equatorial F atom. This Cs structure is more than 2 kcal mol-1 lower in energy than the C2v local minimum at the CCSD(T)/haTZ level of theory. While the interactions between the solvent and ionic solute are quite strong for the monohydrated anions (electronic dissociation energies of ≈12 and ≈24 kcal mol-1 for the SiF5-(H2O)1 and SiF62-(H2O)1 global minima, respectively), these values are nearly perfectly doubled for the dihydrates, with the lowest-energy SiF5-(H2O)2 and SiF62-(H2O)2 minima exhibiting dissociation energies of ≈24 and ≈47 kcal mol-1, respectively. Structures that form hydrogen bonds between the solvating water molecules also exhibit the largest shifts in the harmonic OH stretching frequencies for the waters of hydration. These shifts can exceed -100 cm-1 for the SiF5-(H2O)2 minimum and -300 cm-1 for the SiF62-(H2O)2 minimum relative to an isolated H2O molecule at the CCSD(T)/haTZ level of theory. This work also corrects the OH stretching frequency shifts for two dihydrate minima of PF6- that were previously erroneously reported ( J. Phys. Chem. A 2020, 124, 8744-8752, DOI: 10.1021/acs.jpca.0c06466).
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Affiliation(s)
- Jacquelyn J Mosely
- Department of Chemistry and Biochemistry, University of Mississippi, University, Mississippi 38677-1848, United States
| | - Gregory S Tschumper
- Department of Chemistry and Biochemistry, University of Mississippi, University, Mississippi 38677-1848, United States
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Gousseva E, Towers Tompkins FK, Seymour JM, Parker LG, Clarke CJ, Palgrave RG, Bennett RA, Grau-Crespo R, Lovelock KRJ. Anion-Dependent Strength Scale of Interactions in Ionic Liquids from X-ray Photoelectron Spectroscopy, Ab Initio Molecular Dynamics, and Density Functional Theory. J Phys Chem B 2024; 128:5030-5043. [PMID: 38727250 PMCID: PMC11129296 DOI: 10.1021/acs.jpcb.4c00362] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2024] [Revised: 04/22/2024] [Accepted: 04/22/2024] [Indexed: 05/24/2024]
Abstract
Using a combination of experiments and calculations, we have gained new insights into the nature of anion-cation interactions in ionic liquids (ILs). An X-ray photoelectron spectroscopy (XPS)-derived anion-dependent electrostatic interaction strength scale, determined using XPS core-level binding energies for IL cations, is presented here for 39 different anions, with at least 18 new anions included. Linear correlations of experimental XPS core-level binding energies for IL cations with (a) calculated core binding energies (ab initio molecular dynamics (AIMD) simulations were used to generate high-quality model IL structures followed by single-point density functional theory (DFT) to obtain calculated core binding energies), (b) experimental XPS core-level binding energies for IL anions, and (c) other anion-dependent interaction strength scales led to three main conclusions. First, the effect of different anions on the cation can be related to ground-state interactions. Second, the variations of anion-dependent interactions with the identity of the anion are best rationalized in terms of electrostatic interactions and not occupied valence state/unoccupied valence state interactions or polarizability-driven interactions. Therefore, the XPS-derived anion-dependent interaction strength scale can be explained using a simple electrostatic model based on electrostatic site potentials. Third, anion-probe interactions, irrespective of the identity of the probe, are primarily electrostatic, meaning that our electrostatic interaction strength scale captures some inherent, intrinsic property of anions independent of the probe used to measure the interaction strength scale.
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Affiliation(s)
| | | | - Jake M. Seymour
- Department
of Chemistry, University of Reading, Reading RG6 6DX, U.K.
| | - Lewis G. Parker
- Department
of Chemistry, University of Reading, Reading RG6 6DX, U.K.
| | - Coby J. Clarke
- School
of Chemistry, University of Nottingham, Nottingham NG7 2RD, U.K.
| | - Robert G. Palgrave
- Department
of Chemistry, University College London, London WC1H 0AJ, U.K.
| | - Roger A. Bennett
- Department
of Chemistry, University of Reading, Reading RG6 6DX, U.K.
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3
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Gousseva E, Midgley SD, Seymour JM, Seidel R, Grau-Crespo R, Lovelock KRJ. Understanding X-ray Photoelectron Spectra of Ionic Liquids: Experiments and Simulations of 1-Butyl-3-methylimidazolium Thiocyanate. J Phys Chem B 2022; 126:10500-10509. [PMID: 36455069 PMCID: PMC9761679 DOI: 10.1021/acs.jpcb.2c06372] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Abstract
We demonstrate a combined experimental and computational approach to probe the electronic structure and atomic environment of an ionic liquid, based on core level binding energies. The 1-butyl-3-methylimidazolium thiocyanate [C4C1Im][SCN] ionic liquid was studied using ab initio molecular dynamics, and results were compared against previously published and new experimental X-ray photoelectron spectroscopy (XPS) data. The long-held assumption that initial-state effects in XPS dominate the measured binding energies is proven correct, which validates the established premise that the ground state electronic structure of the ionic liquid can be inferred directly from XPS measurements. A regression model based upon site electrostatic potentials and intramolecular bond lengths is shown to account accurately for variations in core-level binding energies within the ionic liquid, demonstrating the important effect of long-range interactions on the core levels and throwing into question the validity of traditional single ion pair ionic liquid calculations for interpreting XPS data.
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Affiliation(s)
| | - Scott D. Midgley
- Department
of Chemistry, University of Reading, ReadingRG6 6DX, U.K.
| | - Jake M. Seymour
- Department
of Chemistry, University of Reading, ReadingRG6 6DX, U.K.
| | - Robert Seidel
- Helmholtz-Zentrum
Berlin für Materialien und Energie (HZB), Berlin14109, Germany
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Moraes AS, Pinheiro GA, Lourenço TC, Lopes MC, Quiles MG, Dias LG, Da Silva JLF. Screening of the Role of the Chemical Structure in the Electrochemical Stability Window of Ionic Liquids: DFT Calculations Combined with Data Mining. J Chem Inf Model 2022; 62:4702-4712. [PMID: 36122418 DOI: 10.1021/acs.jcim.2c00748] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Ionic liquids have attracted the attention of researchers as possible electrolytes for electrochemical energy storage devices. However, their properties, such as the electrochemical stability window (ESW), ionic conductivity, and diffusivity, are influenced both by the chemical structures of cations and anions and by their combinations. Most studies in the literature focus on the understanding of common ionic liquids, and little effort has been made to find ways to improve our atomistic understanding of those systems. The goal of this paper is to explore the structural characteristics of cations and anions that form ionic liquids that can expand the HOMO/LUMO gap, a property directly linked to the ESW of the electrolyte. For that, we design a framework for randomly generating new ions by combining their fragments. Within this framework, we generate about 104 cations and 104 anions and fully optimize their structures using density functional theory. Our calculations show that aromatic cations are less stable ionic liquids than aliphatic ones, an expected result if chemical rationale is used. More importantly, we can improve the gap by adding electron-donating and electron-withdrawing functional groups to the cations and anions, respectively. The increase can be about 2 V, depending on the case. This improvement is reflected in a wider ESW.
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Affiliation(s)
- Alex S Moraes
- Chemistry Department, Central-West State University, 85040-167 Guarapuava, Paraná, Brazil
| | - Gabriel A Pinheiro
- Institute of Science and Technology, Federal University of São Paulo, 12247-014 São José dos Campos, São Paulo, Brazil
| | - Tuanan C Lourenço
- São Carlos Institute of Chemistry, University of São Paulo, P.O. Box 780, 13560-970 São Carlos, São Paulo, Brazil
| | - Mauro C Lopes
- Chemistry Department, Central-West State University, 85040-167 Guarapuava, Paraná, Brazil
| | - Marcos G Quiles
- Institute of Science and Technology, Federal University of São Paulo, 12247-014 São José dos Campos, São Paulo, Brazil
| | - Luis G Dias
- Chemistry Department, FFCLRP, University of São Paulo, 14040-901 Ribeirão Preto, São Paulo, Brazil
| | - Juarez L F Da Silva
- São Carlos Institute of Chemistry, University of São Paulo, P.O. Box 780, 13560-970 São Carlos, São Paulo, Brazil
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Seymour J, Gousseva E, Large A, Held G, Hein D, Wartner G, Quevedo W, Seidel R, Kolbeck C, Clarke CJ, Fogarty R, Bourne R, Bennett R, Palgrave R, Hunt PA, Lovelock KRJ. Resonant Electron Spectroscopy: Identification of Atomic Contributions to Valence States. Faraday Discuss 2022; 236:389-411. [DOI: 10.1039/d1fd00117e] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Valence electronic structure is crucial for understanding and predicting reactivity. Valence non-resonant X-ray photoelectron spectroscopy (NRXPS) provides a direct method for probing the overall valence electronic structure. However, it is...
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