Applying Computational Spectroscopy Methods to Raman Spectra of Dicationic, Imidazolium-Based, Ionic Liquids.

Studying ionic liquids (ILs) through computational methods is one of the ways to accelerate progress in the design of novel and potentially green materials optimized for task-specific applications. Therefore, it is essential to develop simple and cost-effective computational procedures that are able to replicate and predict experimental data. Among these, spectroscopic measurements are of particular relevance since they are often implicated in structure-property relationships, especially in the infrared spectral region, where characteristic absorption and scattering processes due to molecular vibrations are ultimately influenced by the surrounding environment in the condensed phase.

Thermodynamic Study of 1,4-Bis(3-methylimidazolium-1-yl)butane Bis(trifluoromethylsulfonyl)imide ([C(MIm)][NTf]) from 6 to 350 K.

The molar heat capacity of 1,4-bis(3-methylimidazolium-1-yl)butane bis(trifluoromethylsulfonyl)imide dicationic ionic compound ([C(MIm)][NTf]) has been studied over the temperature range from 6 to 350 K by adiabatic calorimetry. In the above temperature interval, this compound has been found to form crystal, liquid, and supercooled liquid. For [C(MIm)][NTf], the temperature of fusion ° = (337.

Bioderived, chiral and stable 1-dimensional light-responsive nanostructures: Interconversion between tubules and twisted ribbons.

Hypothesis: Self-assembling molecular structures responding to light stimulus are appealing for applications as sensing and drug delivery. Supramolecular nanotubes have a relevant potential in nanotechnology as they can be used to encapsulate different loads like drugs, biological macromolecules, and nanomaterials. In addition, they are suitable elements for novel supracolloidal materials.

Sublimation Study of Six 5-Substituted-1,10-Phenanthrolines by Knudsen Effusion Mass Loss and Solution Calorimetry.

The vapor pressures of six solid 5-X-1,10-phenanthrolines (where X = Cl, CH, CN, OCH, NH, NO) were determined in suitable temperature ranges by Knudsen Effusion Mass Loss (KEML). From the temperature dependencies of vapor pressure, the molar sublimation enthalpies, Δ(⟨⟩), were calculated at the corresponding average ⟨⟩ of the explored temperature ranges. Since to the best of our knowledge no thermochemical data seem to be available in the literature regarding these compounds, the Δ(⟨⟩) values obtained by KEML experiments were adjusted to 298.

Change of Selectivity in C-H Functionalization Promoted by Nonheme Iron(IV)-oxo Complexes by the Effect of the -hydroxyphthalimide HAT Mediator.

A kinetic analysis of the hydrogen atom transfer (HAT) reactions from a series of organic compounds to the iron(IV)-oxo complex [(N4Py)Fe(O)] and to the phthalimide -oxyl radical (PINO) has been carried out. The results indicate that a higher activating effect of α-heteroatoms toward the HAT from C-H bonds is observed with the more electrophilic PINO radical. When the -hydroxy precursor of PINO, hydroxyphthalimide (NHPI), is used as a HAT mediator in the oxidation promoted by [(N4Py)Fe(O)], significant differences in terms of selectivity have been found.

On the Coordination Chemistry of the lanthanum(III) Nitrate Salt in EAN/MeOH Mixtures.

A thorough structural characterization of the La(NO) salt dissolved into several mixtures of ethyl ammonium nitrate (EAN) and methanol (MeOH) with EAN molar fraction χ ranging from 0 to 1 has been carried out by combining molecular dynamics (MD) and X-ray absorption spectroscopy (XAS). The XAS and MD results show that changes take place in the La first solvation shell when moving from pure MeOH to pure EAN. With increasing the ionic liquid content of the mixture, the La first-shell complex progressively loses MeOH molecules to accommodate more and more nitrate anions.

Coordination of the Co and Ni Ions in TfN Based Ionic Liquids: A Combined X-ray Absorption and Molecular Dynamics Study.

Molecular dynamics (MD) simulations and X-ray absorption spectroscopy (XAS) have been combined to study the coordination of the Co and Ni ions in ionic liquids (ILs) based on the bis(trifluoromethylsulfonyl)imide ([TfN]) anion and having different organic cations, namely, 1-butyl-3-methylimidazolium ([Cmim]), 1,8-bis(3-methylimidazolium-1-yl)octane ([C(mim)]), ,,-trimethyl--(2-hydroxyethyl)ammonium ([choline]), and butyltrimethylammonium ([BTMA]). Co and Ni K-edge XAS data have been collected on 0.1 mol L Co(TfN) and Ni(TfN) solutions and on the metallic salts.

Competition Between C -S and C -C Bond Cleavage in β-Hydroxysulfoxides Cation Radicals Generated by Photoinduced Electron Transfer.

A kinetic and product study of the 3-cyano-N-methyl-quinolinium photoinduced monoelectronic oxidation of a series of β-hydroxysulfoxides has been carried out to investigate the competition between C -S and C -C bond cleavage within the corresponding cation radicals. Laser flash photolysis experiments unequivocally established the formation of sulfoxide cation radicals showing their absorption band (λ ≈ 520 nm) and that of 3-CN-NMQ (λ ≈ 390 nm). Steady-state photolysis experiments suggest that, in contrast to what previously observed for alkyl phenyl sulfoxide cation radicals that exclusively undergo C -S bond cleavage, the presence of a β-hydroxy group makes, in some cases, the C -C scission competitive.

Unraveling the solvation geometries of the lanthanum(III) bistriflimide salt in ionic liquid/acetonitrile mixtures.

A synergic approach combining molecular dynamics (MD) and X-ray absorption spectroscopy (XAS) has been used to investigate the structural properties of the La(Tf2N)3 salt (where Tf2N = bistriflimide or bis(trifluoromethansulfonyl)imide) dissolved into several mixtures of acetonitrile and the 1,8-bis(3-methylimidazolium-1-yl)octane bistriflimide (C8(mim)2(Tf2N)2) ionic liquid (IL), with the IL molar fraction (χIL) ranging from 0 to 1. The XAS and MD results show that major changes take place in the La3+ first solvation shell when moving from pure acetonitrile to pure C8(mim)2(Tf2N)2. With increasing the IL concentration of the mixture, the La3+ first shell complex progressively loses acetonitrile molecules to accommodate more and more oxygen atoms of the Tf2N- anions.

-Hydroxyphthalimide: A Hydrogen Atom Transfer Mediator in Hydrocarbon Oxidations Promoted by Nonheme Iron(IV)-Oxo Complexes.

The oxidation of a series of hydrocarbons by the nonheme iron(IV)-oxo complex [(N4Py)Fe═O] is efficiently mediated by -hydroxyphthalimide. The increase of reactivity is associated to the oxidation of the mediator to the phthalimide -oxyl radical, which efficiently abstracts a hydrogen atom from the substrates, regenerating the mediator in its reduced form.

Solvation structure of lanthanide(iii) bistriflimide salts in acetonitrile solution: a molecular dynamics simulation and EXAFS investigation.

A synergic approach combining molecular dynamics (MD) and extended X-ray absorption fine structure (EXAFS) spectroscopy has been used to investigate weak-concentrated (0.1 M) acetonitrile solutions of La(TfN) and Dy(TfN) salts (where TfN is the bis(trifluoromethanesulfonyl)imide). The MD simulations show that contact ion pairs between the Ln cations and the TfN anions are formed in the solutions.

Evaluation of Polar Effects in Hydrogen Atom Transfer Reactions from Activated Phenols.

Evaluation of polar effects in hydrogen atom transfer (HAT) processes is made difficult by the fact that in most cases substrates characterized by lower bond dissociation energies (BDEs), activated from an enthalpic point of view, are also more activated by polar effects. In search of an exception to this general rule, we found that the introduction of a methoxy substituent in the 3-position of 2,6-dimethylphenol results in a small increase in the O-H BDE and a decrease of the ionization potential of the phenol. These findings suggest that the enthalpic effect associated with the addition of the m-methoxy group to 2,6-dimethylphenol will decrease reaction rates, while the polar effects will increase reaction rates.

Oxidative functionalization of aliphatic and aromatic amino acid derivatives with HO catalyzed by a nonheme imine based iron complex.

The oxidation of a series of -acetyl amino acid methyl esters with HO catalyzed by a very simple iminopyridine iron(ii) complex 1 easily obtainable by self-assembly of 2-picolylaldehyde, 2-picolylamine, and Fe(OTf) was investigated. Oxidation of protected aliphatic amino acids occurs at the α-C-H bond exclusively (-AcAlaOMe) or in competition with the side-chain functionalization (-AcValOMe and -AcLeuOMe). -AcProOMe is smoothly and cleanly oxidized with high regioselectivity affording exclusively C-5 oxidation products.

Influence of Counterions on the Hydration Structure of Lanthanide Ions in Dilute Aqueous Solutions.

A synergic approach combining molecular dynamics (MD) simulations and X-ray absorption spectroscopy (XAS) has been used to investigate diluted (0.1 M) aqueous solutions of two lanthanide ions (Ln), namely, La and Dy, with triflate, nitrate, and bis(trifluoromethylsulfonyl)imide (TfN) as counterions. The different complexing ability of the three anions has been highlighted by the analysis of the MD simulations: TfN does not form inner-sphere complexes, while a small amount of triflate coordinates both the La and Dy cations in their first solvation shell.

On the coordination of Zn ion in TfN based ionic liquids: structural and dynamic properties depending on the nature of the organic cation.

A synergic approach combining molecular dynamics (MD) simulations and X-ray absorption spectroscopy has been used to investigate diluted solutions of zinc bis(trifluoromethanesulfonyl)imide (Zn(TfN)) in TfN based ionic liquids (ILs) having different organic cations, namely the 1-butyl-3-methylimidazolium ([C(mim)]), 1,8-bis(3-methylimidazolium-1-yl)octane ([C(mim)]), N,N,N-trimethyl-N-(2-hydroxyethyl)ammonium ([Choline]) and butyltrimethylammonium ([BTMA]) ions. All of the ILs tend to dissolve the Zn(TfN) species giving rise to a different structural arrangement around the Zn as compared to that of the salt crystallographic structure. A quantitative analysis of the Zn K-edge extended X-ray absorption fine structure (EXAFS) spectra of the solutions has been carried out based on the microscopic description of the systems derived from the MD simulations.

Toward the Elucidation of the Competing Role of Evaporation and Thermal Decomposition in Ionic Liquids: A Multitechnique Study of the Vaporization Behavior of 1-Butyl-3-methylimidazolium Hexafluorophosphate under Effusion Conditions.

The evaporation/decomposition behavior of the imidazolium ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMImPF) was investigated in the overall temperature range 425-551 K by means of the molecular-effusion-based techniques Knudsen effusion mass loss (KEML) and Knudsen effusion mass spectrometry (KEMS), using effusion orifices of different size (from 0.2 to 3 mm in diameter). Specific effusion fluxes measured by KEML were found to depend markedly on the orifice size, suggesting the occurrence of a kinetically delayed evaporation/decomposition process.

Hydrogen Atom Transfer (HAT) Processes Promoted by the Quinolinimide-N-oxyl Radical. A Kinetic and Theoretical Study.

A kinetic study of the hydrogen atom transfer (HAT) reactions from a series of organic compounds to the quinolinimide-N-oxyl radical (QINO) was performed in CHCN. The HAT rate constants are significantly higher than those observed with the phthalimide-N-oxyl radical (PINO) as a result of enthalpic and polar effects due to the presence of the N-heteroaromatic ring in QINO. The relevance of polar effects is supported by theoretical calculations conducted for the reactions of the two N-oxyl radicals with toluene, which indicate that the HAT process is characterized by a significant degree of charge transfer permitted by the π-stacking that occurs between the toluene and the N-oxyl aromatic rings in the transition state structures.

Aerobic Oxidation of 4-Alkyl-N,N-dimethylbenzylamines Catalyzed by N-Hydroxyphthalimide: Protonation-Driven Control over Regioselectivity.

A change in regioselectivity has been observed in the hydrogen atom transfer (HAT) reactions from 4-alkyl-N,N-dimethylbenzylamines (alkyl = ethyl, isopropyl, and benzyl) to the phthalimide N-oxyl radical (PINO) by effect of protonation. This result can be rationalized on the basis of an acid-induced deactivation of the C-H bonds α to nitrogen toward HAT to PINO as evidenced by the 10-10-fold decrease in the HAT rate constants in acetonitrile following addition of 0.1 M HClO.

Electron Transfer Mechanism in the Oxidation of Aryl 1-Methyl-1-phenylethyl Sulfides Promoted by Nonheme Iron(IV)-Oxo Complexes: The Rate of the Oxygen Rebound Process.

The oxidation of aryl 1-methyl-1-phenylethyl sulfides promoted by the nonheme iron(IV)-oxo complexes [(N4Py)Fe═O] and [(Bn-TPEN)Fe═O] occurs by an electron transfer-oxygen rebound (ET-OT) mechanism leading to aryl 1-methyl-1-phenylethyl sulfoxides accompanied by products derived from C-S fragmentation of sulfide radical cations (2-phenyl-2-propanol and diaryl disulfides). For the first time, the rate constants for the oxygen rebound process (k), which are in the range of <0.8 × 10 to 3.

Kinetic Study of the Reaction of the Phthalimide-N-oxyl Radical with Amides: Structural and Medium Effects on the Hydrogen Atom Transfer Reactivity and Selectivity.

A kinetic study of the hydrogen atom transfer (HAT) reactions from a series of secondary N-(4-X-benzyl)acetamides and tertiary amides to the phthalimide-N-oxyl radical (PINO) has been carried out. The results indicate that HAT is strongly influenced by structural and medium effects; in particular, the addition of Brønsted and Lewis acids determines a significant deactivation of C-H bonds α to the amide nitrogen of these substrates. Thus, by changing the reaction medium, it is possible to carefully control the regioselectivity of the aerobic oxidation of amides catalyzed by N-hydroxyphthalimide, widening the synthetic versatility of this process.

Structural properties of geminal dicationic ionic liquid/water mixtures: a theoretical and experimental insight.

The structural behavior of geminal dicationic ionic liquid 1,n-bis[3-methylimidazolium-1-yl] alkane bromide ([Cn(mim)2]Br2)/water mixtures has been studied using extended X-ray absorption fine structure (EXAFS) spectroscopy in combination with molecular dynamics (MD) simulations. The properties of the mixtures are investigated as a function of both water concentration and alkyl-bridge chain length. The very good agreement between the EXAFS experimental data and the theoretical curves calculated from the MD structural results has proven the validity of the theoretical framework used for all of the investigated systems.

Oxidation of Aryl Diphenylmethyl Sulfides Promoted by a Nonheme Iron(IV)-Oxo Complex: Evidence for an Electron Transfer-Oxygen Transfer Mechanism.

The oxidation of a series of aryl diphenylmethyl sulfides (4-X-C6H4SCH(C6H5)2, where X = OCH3 (1), X = CH3 (2), X = H (3), and X = CF3 (4)) promoted by the nonheme iron(IV)-oxo complex [(N4Py)Fe(IV)═O](2+) occurs by an electron transfer-oxygen transfer (ET-OT) mechanism as supported by the observation of products (diphenylmethanol, benzophenone, and diaryl disulfides) deriving from α-C-S and α-C-H fragmentation of radical cations 1(+•)-4(+•), formed besides the S-oxidation products (aryl diphenylmethyl sulfoxides). The fragmentation/S-oxidation product ratios regularly increase through a decrease in the electron-donating power of the aryl substituents, that is, by increasing the fragmentation rate constants of the radical cations as indicated by a laser flash photolysis (LFP) study of the photochemical oxidation of 1-4 carried out in the presence of N-methoxyphenanthridinium hexafluorophosphate (MeOP(+)PF6(-)).

C-H Bond Oxidation Catalyzed by an Imine-Based Iron Complex: A Mechanistic Insight.

A family of imine-based nonheme iron(II) complexes (LX)2Fe(OTf)2 has been prepared, characterized, and employed as C-H oxidation catalysts. Ligands LX (X = 1, 2, 3, and 4) stand for tridentate imine ligands resulting from spontaneous condensation of 2-pycolyl-amine and 4-substituted-2-picolyl aldehydes. Fast and quantitative formation of the complex occurs just upon mixing aldehyde, amine, and Fe(OTf)2 in a 2:2:1 ratio in acetonitrile solution.

Isotope effect profiles in the N-demethylation of N,N-dimethylanilines: a key to determine the pK(a) of nonheme Fe(III)-OH complexes.

N-demethylation of N,N-dimethylanilines promoted by [(N4Py)Fe(IV)=O](2+) occurs by an electron transfer-proton transfer (ET-PT) mechanism with a rate determining PT step. From the bell-shaped curve of the KDIE profile it has been estimated that the pK(a) of [(N4Py)Fe(III)-OH](2+) is 9.7.