A new comprehensive Molecular Dynamics study using large simulation boxes has been performed in order to complete and extend the structural analysis on the mesoscopic segregation observed in the ...ionic liquids of the 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide homologous series, C n C1imNtf2 (2 ≤ n ≤ 10). The analysis includes the discussion along the whole family of the corresponding structure factors, S(q), in the low-q range (1.6 ≤ q/nm–1 ≤ 20); the confirmation of the periodicity of the polar network of the ionic liquid and its intermediate low-q peak equivalence; and the introduction of five statistical functions that probe the existence and characterize the polar network and the nonpolar aggregates that are formed along the C n C1imNtf2 series. The later functions comprise aggregate size distributions, average number of contact neighbors within an aggregate, neighbor distributions, distributions of aggregate maximum length, and distributions of aggregate volume.
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This paper focuses in the influence of halogen atoms in the design and structural control of the crystal packing of Group VIII halogenated metallocenes. The study is based on the present knowledge on ...new types of intermolecular contacts such as halogen (X⋯X, C-X⋯H, C-X⋯π), π⋯π, and C-H⋯π interactions. The presence of novel C-H⋯M interactions is also discussed. Crystal packings are analysed after database search on this family of compounds. Results are supported by ab initio calculations on electrostatic charge distributions; Hirshfeld analysis is also used to predict the types of contacts to be expected in the molecules. Special attention is given to the competition among hydrogen and halogen interactions, mainly its influence on the nature and geometric orientations of the different supramolecular motifs. Supramolecular arrangements of halogenated metallocenes and Group IV di-halogenated bent metallocenes are also compared and discussed. Analysis supports halogen bonds as the predominant interactions in defining the crystal packing of bromine and iodine 1,1'-halometallocenes.
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Many chemical processes rely extensively on organic solvents posing safety and environmental concerns. For a successful transfer of some of those chemical processes and reactions to aqueous media, ...agents acting as solubilizers, or phase-modifiers, are of central importance. In the present work, the structure of aqueous solutions of several ionic liquid systems capable of forming multiple solubilizing environments were modeled by molecular dynamics simulations. The effect of small aliphatic chains on solutions of hydrophobic 1-alkyl-3-methylimidazolium bis(trifluoromethyl)sulfonylimide ionic liquids (with alkyl = propyl C3C1imNTf2, butyl C4C1imNTf2 and isobutyl iC4C1imNTf2) are covered first. Next, we focus on the interactions of sulphonate- and carboxylate-based anions with different hydrogenated and perfluorinated alkyl side chains in solutions of C2C1imCnF2n+1SO3, C2C1imCnH2n+1SO3, C2C1imCF3CO2 and C2C1imCH3CO2 (n = 1, 4, 8). The last system considered is an ionic liquid completely miscible with water that combines the cation N-methyl-N,N,N-tris(2-hydroxyethyl)ammonium N1 2OH 2OH 2OH+, with high hydrogen-bonding capability, and the hydrophobic anion NTf2–. The interplay between short- and long-range interactions, clustering of alkyl and perfluoroalkyl tails, and hydrogen bonding enables a wealth of possibilities in tailoring an ionic liquid solution according to the needs.
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The functionalization of polymers with sulfonate groups has many important uses, ranging from biomedical applications to detergency properties used in oil-recovery processes. In this work, several ...ionic liquids (ILs) combining 1-alkyl-3-methylimidazolium cations C
C
im
(4 ≤
≤ 8) with alkyl-sulfonate anions C
SO
(4 ≤
≤ 8) have been studied using molecular dynamics simulations, totalizing nine ionic liquids belonging to two homologous series. The radial distribution functions, structure factors, aggregation analyses, and spatial distribution functions reveal that the increase in aliphatic chain length induces no significant change in the structure of the polar network of the ILs. However, for imidazolium cations and sulfonate anions with shorter alkyl chains, the nonpolar organization is conditioned by the forces acting on the polar domains, namely, electrostatic interactions and hydrogen bonding.
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Anion-driven, nanoscale polar-apolar structural organization is investigated in a solvate ionic liquid (SIL) setting by comparing sulfonate-based anions with long and short perfluorinated alkyl ...chains. Representative SILs are created from 1,2-bis(2-methoxyethoxy)ethane ("triglyme" or "G3"), lithium nonafluoro-1-butanesulfonate, and lithium trifluoromethanesulfonate. Molecular dynamics simulations, density functional theory computations, and vibrational spectroscopy provide insight into the overall liquid structure, cation-solvent interactions, and cation-anion association. Significant competition between G3 and anions for cation-binding sites characterizes the G3-LiC
F
SO
mixtures. Only 50% of coordinating G3 molecules form tetradentate complexes with Li
in (G3)
LiC
F
SO
. Moreover, the SIL is characterized by extensive amounts of ion pairing. Based on these observations, (G3)
LiC
F
SO
is classified as a "poor" SIL, similar to the analogous (G3)
LiCF
SO
system. Even though the comparable basicity of the CF
SO
and C
F
SO
anions leads to similar SIL classifications, the hydrophobic fluorobutyl groups support extensive apolar domain formation. These apolar moieties permeate throughout (G3)
LiC
F
SO
and persist even at relatively low dilution ratios of (G3)
LiC
F
SO
. By way of comparison, the CF
group is far too short to sustain polar-apolar segregation. This demonstrates how chemically modifying the anions to include hydrophobic groups can impart unique nanoscale organization to a SIL. Moreover, tuning these nano-segregated fluorinated domains could, in principle, control the presence of dimensionally ordered states in these mixtures without changing the coordination of the lithium ions.
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Ionic-liquid (IL) mixtures hold great promise, as they allow liquids with a wide range of properties to be formed by mixing two common components rather than by synthesizing a large array of pure ILs ...with different chemical structures. In addition, these mixtures can exhibit a range of properties and structural organization that depend on their composition, which opens up new possibilities for the composition-dependent control of IL properties for particular applications. However, the fundamental properties, structure, and dynamics of IL mixtures are currently poorly understood, which limits their more widespread application. This article presents the first comprehensive investigation into the bulk and surface properties of IL mixtures formed from two commonly encountered ILs: 1-ethyl-3-methylimidazolium and 1-dodecyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (C2mimTf2N and C12mimTf2N). Physical property measurements (viscosity, conductivity, and density) reveal that these IL mixtures are not well described by simple mixing laws, implying that their structure and dynamics are strongly composition dependent. Small-angle X-ray and neutron scattering measurements, alongside molecular dynamics (MD) simulations, show that at low mole fractions of C12mimTf2N, the bulk of the IL is composed of small aggregates of C12mim+ ions in a C2mimTf2N matrix, which is driven by nanosegregation of the long alkyl chains and the polar parts of the IL. As the proportion of C12mimTf2N in the mixtures increases, the size and number of aggregates increases until the C12 alkyl chains percolate through the system and a bicontinuous network of polar and nonpolar domains is formed. Reactive atom scattering-laser-induced fluorescence experiments, also supported by MD simulations, have been used to probe the surface structure of these mixtures. It is found that the vacuum–IL interface is enriched significantly in C12 alkyl chains, even in mixtures low in the long-chain component. These data show, in contrast to previous suggestions, that the C12mim+ ion is surface active in this binary IL mixture. However, the surface does not become saturated in C12 chains as its proportion in the mixtures increases and remains unsaturated in pure C12mimTf2N.
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A series of Molecular Dynamics simulations are used to probe the structural features of the 1-alkyl-3-methylimidazolium hexafluorophosphate ionic liquid family CnC1imPF6 (n=3, 6, 9, 12). The ...structural analysis results — structure factor functions, pair radial distribution functions, and aggregate analyses — are compared with previous results obtained for the well-known CnC1imNTf2 series. Equimolar mixtures of (CmC1imPF6+CnC1imPF6) with m/n=3/9, 3/12, 6/9 and 6/12 are also studied and their structure is investigated using the same analysis techniques.
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•Exploring the structure of ionic liquids (ILs) via Molecular Dynamics simulations.•Using differential analyses to access the structural changes along two ionic liquid homologous series.•Understanding the non-homogeneous nature of the nonpolar domains of mixtures of two ILs with different sizes of alkyl chain.
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Small-angle neutron scattering experiments, supported by molecular dynamics simulations, have been performed on a range of compositions of the C
mim
C
mim
Tf
N ionic liquid mixture system. Isotopic ...contrast variation, through selective deuteration of both cations, has been used to assist in fitting the data to different scattering models. These data, and subsequent fitting, show that the structure of the ionic liquid mixtures changes substantially as a function of composition. Mixtures where x < 0.32 are dominated by aggregates of amphiphilic C
mim
ions in the relatively polar C
mimTf
N solvent. Compositions where x > 0.32 can be described as bicontinuous, containing networks of both polar and non-polar domains, where the C12 chains of the C
mim
ions percolate through the system to form a continuous non-polar sub-phase. Temperature-dependent scattering experiments suggest that there is relatively little change in bulk structure in these liquids between 20 and 60 °C. The presence of water, however, does influence some aspects of the liquid structure in a composition that is rich in C
mimTf
N (where x = 0.24).
At 298 K, the surface tension of ionic liquids (ILs) of the 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide series, C n C1ImNTf2, ranges from around 35 mN·m–1 for C2C1ImNTf2 to just ...below 30 mN·m–1 for C12C1ImNTf2. However, the decrease rate along the series is not constant: a large decrease from C2C1ImNTf2 to C8C1ImNTf2 is followed by almost constant values from C8C1ImNTf2 to C12C1ImNTf2. Such behavior is hard to interpret from a molecular point of view without suitable information about the free-surface structure of the different ILs. In this work, we have successfully used the Langmuir principle in combination with structural data obtained from angle-resolved X-ray photoelectron spectroscopy experiments and molecular dynamics simulations, to predict the correct surface tension trend along the IL series. The concepts unveiled for this particular homologous IL family can be easily extended to other systems.
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