Infrared Spectroscopy of Li + Solvation in Diglyme: Ab Initio Molecular Dynamics and Experiment
Not Available
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Engineering topics
Maroncelli, Mark
Publications and source records attributed to Maroncelli, Mark.
Ion Solvation and Hydrogen Bonding in Liquid Electrolytes
The primary goal of the proposed research was to explore the use of far-infrared (FIR) spectroscopy for providing new informal on about the solvation structure and dynamics of small ions such as Li + , Na + , and Mg 2+ in electrolyte solutions commonly used in energy-related applications. Classical and ab initio molecular dynamics simulations were to be carried out together with spectroscopic measurements to aid interpretation of the spectra generated.
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Infrared Spectroscopy of Li + Solvation in EmimBF 4 and in Propylene Carbonate: Ab Initio Molecular Dynamics and Experiment
Infrared (IR) spectra of solutions of the lithium salt LiBF 4 in the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate (EmimBF 4 ) and in the organic solvent propylene carbonate (PC) are studied via infrared spectroscopy and ab initio molecular dynamics (AIMD) simulations. The measurements show that the major effects of LiBF 4 in both solutions, compared to their neat counterparts, are the appearance of a new broad band in the 300-450 cm -1 frequency region and a broadening of the IR structure in the 900-1200 cm -1 region with the development of a new peak at 980 cm -1 . Computational analysis indicates that hindered translational motions of Li + in its solvation cage are mainly responsible for the former, while the latter is due to Li + -induced structural changes and accompanying vibrational frequency shifts of constituent ions and molecules of the solutions. In addition, molecular motions in these and lower frequency regions are generally correlated, disclosing the collective nature of the vibrational dynamics, which involve multiple ions/molecules. Herein, detailed analysis of these features via AIMD simulations of the spectrum and its components arising from auto- and cross-correlations of motions of constituent molecular species, combined with generalized normal modes of the solutions and normal modes of small Li + -containing clusters, is presented. Furthermore, other minor spectral changes caused by the lithium salt as well as the interaction-induced effect on IR spectra are also discussed.
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Rapid water dynamics structures the OH-stretching spectra of solitary water in ionic liquids and dipolar solvents
In a recent study [J. Phys. Chem. B 126, 4584–4598 (2022)], we have used infrared spectroscopy to investigate the solvation and dynamics of solitary water in ionic liquids and dipolar solvents. Complex shapes observed for water OH-stretching bands, common to all high-polarity solvents, were assigned to water in several solvation states. Here, in the present study, classical molecular dynamics simulations of a single water molecule in four ionic liquids and three dipolar solvents were used to test and refine this interpretation. Consistent with past assignments, simulations show solitary water usually donates two hydrogen bonds to distinct solvent molecules. Such symmetrically solvated water produces the primary pair of peaks identified in the OH spectra of water in nearly all solvents. We had further proposed that additional features flanking this main peak are due to asymmetric solvation states, states in which only one OH group makes a hydrogen bond to solvent. Such states were found in significant concentrations in all of the systems simulated. Simulations of the OH stretching spectra using a semiclassical description and the vibrational map developed by Auer and Skinner [J. Chem. Phys. 128, 224511–224512 (2008)] provided semi-quantitative agreement with experiment. Analysis of species-specific spectra confirmed assignment of the additional features in the experimental spectra to asymmetrically solvated water. The simulations also showed that rapid water motions cause a marked motional narrowing compared with the inhomogeneous limit. This narrowing is largely responsible for making the additional features due to minority solvation states manifest in the spectra.
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Electron Transfer Kinetics between an Electron-Accepting Ionic Liquid and Coumarin Dyes
Not provided.
Chemistry↗
n -Decyltrimethylammonium bromide
The title compound, C 13 H 30 N + •Br – (systematic name: N,N,N -trimethyl-1-decanaminium bromide), forms crystals having a bilayer structure, comprised of layers of trimethylammonium cations and bromide anions separated by the inter-digitated n -decyl groups of the cation; close ammonium-methyl-C—H···Br contacts connect the ions. The n -decyl chain adopts a slightly distorted all- trans conformation. The n -decyl chain exhibits positional disorder with all atoms at half occupancy. The sample was a racemic twin.
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Solvent controlled intramolecular electron transfer in mixtures of 1-butyl-3-methylimidizolium tetrafluoroborate and acetonitrile
Time-resolved emission techniques were used to study the excited-state intramolecular electron transfer of 9-(4-biphenyl)-10-methylacridinium (BPAc+) in mixtures of 1-butyl-3-methylimidizolium tetrafluoroborate ([Im 41 ][BF 4 ])+ acetonitrile (ACN), a mixture previously shown to be of nearly constant polarity and nearly ideal mixing behavior. Reaction times (τ rxn ) track solvation times (τsolv) as a function of mixture composition over a range of more than 3 orders of magnitude in τ solv . This same correlation extends to a variety of neat dipolar solvents and ionic liquids. Reaction times are ∼2-fold larger than τ solv over most of the range studied but appear to reach a limiting value of ∼3 ps in the fastest solvents.
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Photoinduced Bimolecular Electron Transfer in Ionic Liquids: Cationic Electron Donors
Recently, we have reported a systematic study of photoinduced electron-transfer reactions in ionic liquid solvents using neutral and anionic electron donors and a series of cyano-substituted anthracene acceptors [Wu, B.; Maroncelli, M.; Castner, E. W., Jr.Photoinduced Bimolecular Electron Transfer in Ionic Liquids. J. Am. Chem. Soc.139, 2017, 14568]. In this paper, we report complementary results for a cationic class of 1-alkyl-4-dimethylaminopyridinium electron donors. Reductive quenching of cyano-substituted anthracene fluorophores by these cationic quenchers is studied in solutions of acetonitrile and the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. Varying the length of the alkyl chain permits tuning of the quencher diffusivities in solution. The observed quenching kinetics are interpreted using a diffusion-reaction analysis. Finally, together with results from the prior study, these results show that the intrinsic electron-transfer rate constant does not depend on the quencher charge in this family of reactions.
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Physical Chemistry of Reaction Dynamics in Ionic Liquid
Work completed over the past year mainly involves finishing studies related to solvation dynamics in ionic liquids, amplifying and extending our initial PFG-NMR work on solute diffusion, and learning how to probe rotational dynamics in ionic liquids.
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Photoinduced Bimolecular Electron Transfer from Cyano Anions in Ionic Liquids
Not Available
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2-Cyano-3-(2,3,6,7-tetrahydro-1 H ,5 H -benzo[ ij ]quinolizin-9-yl)prop-2-enoic acid dimethyl sulfoxide monosolvate
In dimethyl sulfoxide solvated 9-(2-carboxy-2-cyanovinyl)- julolidine, C16H16N2O2C2H6OS, the essentially planar – CH (CN)–CO2H substituent (r.m.s. deviation = 0.014 A° ) is almost coplanar with respect to the benzene ring, the dihedral angle between the two planes being 0.48 (2). The conformations of the fused, non-aromatic rings were found to be halfchair. In the crystal, the acid molecule forms a hydrogen bond to the O atom of the solvent molecule. The acid molecule is disordered over two positions with respect to the methylene C atoms in a 1:1 ratio. The crystal studied was found to be a racemic twin.
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Solvation and Reaction in Ionic Liquids
The long-range goal of our DOE-sponsored research is to obtain a fundamental understanding of solvation effects on photo-induced charge transfer and related processes. Much of the focus during the past funding period has been on studies of ionic liquids and on characterizing various reactions with which to probe the nature of this interesting new solvent medium.
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Electronic Spectroscopy & Dynamics
The Gordon Research Conference (GRC) on Electronic Spectroscopy and Dynamics was held at Colby College, Waterville, NH from 07/19/2009 thru 07/24/2009. The Conference was well-attended with participants (attendees list attached). The attendees represented the spectrum of endeavor in this field coming from academia, industry, and government laboratories, both U.S. and foreign scientists, senior researchers, young investigators, and students. The GRC on Electronic Spectroscopy & Dynamics showcases some of the most recent experimental and theoretical developments in electronic spectroscopy that probes the structure and dynamics of isolated molecules, molecules embedded in clusters and condensed phases, and bulk materials. Electronic spectroscopy is an important tool in many fields of research, and this GRC brings together experts having diverse backgrounds in physics, chemistry, biophysics, and materials science, making the meeting an excellent opportunity for the interdisciplinary exchange of ideas and techniques. Topics covered in this GRC include high-resolution spectroscopy, biological molecules in the gas phase, electronic structure theory for excited states, multi-chromophore and single-molecule spectroscopies, and excited state dynamics in chemical and biological systems.
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