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An insight into the intermolecular vibrational modes of dicationic ionic liquids through far-infrared spectroscopy and DFT calculations.

ABSTRACT: Dicationic ionic liquids (DILs) are a subclass of the ionic liquid (IL) family and are characterized by two cationic head groups linked by means of a spacer. While DILs are increasingly attracting interest due to their peculiar physico-chemical properties, there is still a lack of understanding of their intermolecular interactions. Herein, we report our investigations on the intermolecular vibrational modes of two bromide DILs and of a bistriflimide DIL. The minimal possible neutral cluster of ions was studied as a simplified model of these systems and was optimized at the DFT level. Normal modes of two sandwich-like conformers were then calculated using the harmonic approximation with analytical computation of the second derivatives of molecular energy with respect to the atomic coordinates. The calculated spectra were compared to far-infrared experimental spectra and two groups of peaks over three, for the two bromide DILs, and three over five, for the Tf₂N^- DIL, were described by the proposed neutral cluster model. Therefore, this model represents a reliable and computationally affordable model for the exploration of the intermolecular interactions of this kind of system.

SUBMITTER: Guglielmero L

PROVIDER: S-EPMC9072084 | biostudies-literature | 2019 Sep

REPOSITORIES: biostudies-literature

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An insight into the intermolecular vibrational modes of dicationic ionic liquids through far-infrared spectroscopy and DFT calculations.

Guglielmero Luca L Guazzelli Lorenzo L Toncelli Alessandra A Chiappe Cinzia C Tredicucci Alessandro A Pomelli Christian Silvio CS

RSC advances 20190925 52

Dicationic ionic liquids (DILs) are a subclass of the ionic liquid (IL) family and are characterized by two cationic head groups linked by means of a spacer. While DILs are increasingly attracting interest due to their peculiar physico-chemical properties, there is still a lack of understanding of their intermolecular interactions. Herein, we report our investigations on the intermolecular vibrational modes of two bromide DILs and of a bistriflimide DIL. The minimal possible neutral cluster of i ...[more]

PMID: 35530250

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Project description:In this work, the configuration and stability of 15 geminal dicationic ionic liquids (GDILs) and their adsorption mechanism on the graphene nanoflake (GNF) are investigated using the density functional theory (DFT) method. We find that the interactions of dications ([DAm]+, [DIm]+, [DImDm]+, [DPy]+, and [DPyrr]+)) are stabilized near the anions ([BF4]-, [PF6]-, and [Tf2N]-) in the most stable configurations of GDILs through electrostatic interactions, van der Waals (vdW) interactions, and hydrogen bonding (H-bonding). Our calculations show that the adsorption of the GDILs on the GNF is consistent with the charge transfer and occurs via X···π (X = N, O, F), C-H···π, and π···π noncovalent interactions, leading to a decrease in the strength of the intermolecular interactions between the dications and anions in the GDILs. The thermochemistry calculations reveal that the formation of GDIL@GNF complexes is an exothermic and favorable reaction. The adsorption energy (Eads) calculations show that the highest Eads values for the interaction of GDILs containing [BF4]-, [PF6]-, and [Tf2N]- anions with the GNF are observed for the [DPy][BF4]@GNF (-23.56 kcal/mol), [DPy][PF6]@GNF (-29.29 kcal/mol), and [DPyrr][Tf2N]@GNF (-24.74 kcal/mol) complexes, respectively. Our results show that the adsorption of the GDILs on the GNF leads to the decrease of the chemical potential (μ), chemical hardness (η), and HOMO-LUMO energy gap (Eg) values and an increase in the electrophilicity index (ω) value of the GNF. In addition, the effect of GDIL adsorption on the UV-vis absorption spectrum was studied at the TD-M06-2X/cc-pVDZ level of theory. We find that the adsorption of GDILs results in minimal change in the shape of the main absorption peak (at λ = 363 nm) in the GNF spectrum and only shifts it to higher wavelengths. On the other hand, a new peak appears in the GNF spectrum upon adsorption of [DPy][Y] (Y = [BF4]-, [PF6]-, and [Tf2N]-) due to the relatively strong π···π interactions between the [DPy]+ dication and GNF. Finally, the transition density matrix (TDM) heat maps show that electron transfers related to the excitation states in the GDIL@GNF complexes occur mainly through π(C=C) → π*(C=C) transitions in the GNF and the transitions from [DPy]+ dication to the GNF.

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An insight into the intermolecular vibrational modes of dicationic ionic liquids through far-infrared spectroscopy and DFT calculations.

Publications

An insight into the intermolecular vibrational modes of dicationic ionic liquids through far-infrared spectroscopy and DFT calculations.

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