Europium-based ionic liquids as luminescent soft materials

Tailoring refractive index dispersion in ionic liquids: The influence of charge delocalization in cations

In this work, we study the contributions that different molecular blocks have in the wavelength-dependence of the refractive index in ionic liquids. The ionic liquids chosen for this work are combinations of the bis(trifluoromethylsulfonyl)imide anion with cations based on four different heterocycles with different extents of charge delocalization. The analysis is performed in terms of the experimental electronic polarizability, which is obtained by combining measurements of refractive index curves and densities via the Lorentz-Lorenz equation. Exploiting the additivity of electronic polarizability in ionic liquids, the contribution of the anion and the heterocycles of the cations is separated from that of the alkyl chains. Our results show important differences in these contributions, revealing a key influence of the charge delocalization in the cationic rings on the behavior of the refractive index dispersion. The understanding of how different parts of ionic liquids affect their refractive index dependence on wavelength would allow to gain precise control of this magnitude, enabling the development of customized optical materials for diverse applications in photonics and sensing technologies.

Magnetic resonance imaging: an innovative approach to observe rare metal extraction using ionic liquid

In the present work, a novel approach has been made to evaluate the extraction mechanism of neodymium (Nd) using trihexyl-tetradecyl-phosphonium benzoate (TTPB) ionic liquid through nuclear magnetic resonance (NMR) techniques. A detailed study on the interactions between the extractant (Nd) and the ionic liquid (IL) is presented. The 1H NMR spectral analysis confirmed that Nd extraction took place through the benzoate anion. Furthermore, the NMR relaxation time of the anion is greatly affected affirming that Nd extraction indeed took place through the benzoate anion. This change in the relaxation time caused by the Nd ion on the protons in the anion and cation in TTPB has been used to visualize the extraction mechanism using 1H MRI. A strong change in the image intensity with respect to the time observed in the IL phase validates the extraction of Nd from the aqueous phase into the IL phase. Also, combining the 1H NMR, diffusion coefficient, Karl-Fischer and ultraviolet-visible absorption spectroscopic (UV-Vis) results, we have elucidated the co-ordination structure around Nd during the extraction process.

Boosting the Luminescence of a Europium(III)-β-Diketonate Complex-Nanoclay Aqueous Solution by Acetylcholine

It is a challenging task to prepare lanthanide complex-based luminescent materials with high quantum efficiency in aqueous solution, since the excited state of Ln3+ can be significantly quenched by water through the excitation of the O-H vibrations. Herein, we present a simple and environmentally friendly strategy to prepare strongly red-light-emitting lanthanide complex-based luminescent materials by loading 2-thenoyltrifluoroacetate (TTA) on the Eu3+-exchanged nanoclay (Eu3+(TTAn)-NC, NC = nanoclay) and coadsorption of choline chloride (ChCl) or acetylcholine chloride (AChCl) in water. The coadsorbed molecules remarkably boosted the luminescence of Eu3+(TTAn)-NC, which is tentatively ascribed to the removal of waters coordinated in the Eu3+ coordination sphere via the complete coordination of TTA mediated by ChCl or AChCl. Highly luminescent films were facilely prepared by mixing a Eu3+(TTAn)-NC aqueous solution with PVA-ChCl (PVA-AChCl) deep eutectic solvents. This work provides a simple and environmentally friendly way for preparing highly luminescent emitting luminescent materials in aqueous solution.

Synthesis, Characterization, and Magnetic Properties of Lanthanide-Containing Paramagnetic Ionic Liquids: An Evan's NMR Study

The present study focuses on the synthesis and characterization of lanthanide-containing paramagnetic ionic liquids (ILs), [CnC1Im]3[MCl3X3] (n = 4, 6, and 8; M = Gd, Dy, and Ho; X = Br and Cl), derived from 1-alkyl-3-methylimidazolium anions. These paramagnetic ILs exhibit low vapor pressure, high thermal stability, physiochemical stability, and tunability, along with significant magnetic susceptibility, making them of interest in advanced material applications that may take advantage of neat liquids with magnetic susceptibility. Structural and physical properties were determined using FTIR, 1H NMR, DSC, and TGA. The room temperature density and viscosity of the iron paramagnetic ILs were also reported. Accompanying this report of paramagnetic IL products, we reintroduce and highlight Evan's NMR technique, an accessible magnetic susceptibility measurement technique that can utilize any available proton NMR to characterize the magnetic susceptibility of ILs. This work demonstrates the robustness of Evan's technique by demonstrating the ability to account for the IL water content, a common issue for hygroscopic materials, during the measurement of magnetic susceptibility. A detailed comparison of the ILs is presented, with dysprosium- and holmium-containing paramagnetic ILs exhibiting the highest magnetic susceptibility reported for mononuclear ILs reported to date. These materials have been studied with an eye on applications for mass transfer, eventually seeking to optimize magnetic susceptibility and viscosity using magnetic field gradients to move paramagnetic ILs carrying solute or heat. The study of paramagnetic ILs is important not only for understanding the magnetic properties of these materials but also for potential applications in areas such as magnetic resonance imaging, biomedicine, environmental remediation, and mass transfer. These unique materials have the potential to bring about new advances and technologies in the fields of materials science and analytical chemistry.

Low-melting multicharge ionic liquids with [Ln(NO3)5]2- (Ln = Ho-Lu): structural, electrostatic, thermochemical, and fluorescence properties

A series of green and safe heavy-rare-earth ionic liquids were obtained using a straightforward method. The stable structures of these ionic liquids, characterized by high-coordinating anions, were confirmed by nuclear magnetic resonance (NMR) spectroscopy, infrared (IR) spectroscopy, and single crystal X-ray diffraction (XRD). These ionic liquids exhibited wide liquid phase intervals and excellent thermal stability. The bidentate nitrato ligands occupied a sufficient number of coordination sites on the lanthanide ions, resulting in the formation of water-free 10-coordination structures. To explain the anomalous melting points observed in these multi-charged ionic liquids, a combination of experimental data and theoretical studies was employed to investigate the relationship between the electrostatic properties and the melting point. The electrostatic potential density per unit ion surface and volume were proposed and utilized for melting point prediction, demonstrating good linearity. Furthermore, the coordinating spheres of the lanthanide ions in these ionic liquids were devoid of luminescence quenchers such as O-H and N-H groups. Notably, the ionic liquids containing Ho³⁺, Er³⁺, and Tm³⁺ exhibited long lifetime near-infrared (NIR) and blue emissions, respectively. The UV-vis-NIR spectra revealed numerous electronic transitions of the lanthanide ions, which were attributed to their unique optical properties.

Designing Dimeric Lanthanide(III)-Containing Ionic liquids

Herein, we report on the preparation of liquid dimeric lanthanide(III)-containing compounds. Starting from the design of dimeric solids, we demonstrate that by tuning of anion and cation structures we can lower the melting points below room temperature, whilst maintaining the dimeric structure. Magnetic measurements could establish the spin-spin interactions of the neighboring lanthanide(III) ions in the liquid state at low temperatures, and matched the interactions of the analogous crystalline solid compounds.

Synthesis of Novel Luminescent Double-Decker Silsesquioxanes Based on Partially Condensed TetraSilanolPhenyl POSS and Tb3+/Eu3+ Lanthanide Ions

In this study, novel lanthanide-containing double-decker polyhedral oligomeric silsesquioxanes (POSS) were prepared by combining the partially condensed TetraSilanolPhenyl POSS with terbium (Tb3+) and europium (Eu3+) ions. This open-cage POSS possesses four diametrically opposite silanol groups that are able to coordinate, under mild conditions, different luminescent ions through a simple corner-capping method. The two metal-containing POSS functionalized with Tb3+ and with an equimolar combination of Tb3+ and Eu3+ show a completely condensed structure with different luminescent properties. Their emission features depend on the chemical nature of the metal ions incorporated in the framework. An improved stokes shift was detected in the bimetallic compound containing both the Tb3+ and Eu3+ ions, promoted by the occurrence of a Tb3+→Eu3+ energy transfer mechanism. These characteristics identify this metal-functionalized silica platform as a potential candidate for the development of novel luminescent devices.

Magnetic, Photo- and Electroluminescent: Multifunctional Ionic Tb Complexes

In the search for new multifunctional materials, particularly for application in solid-state lighting, a set of terbium salicylato (Sal) complexes of general composition [Cat][Tb(Sal)₄] with the commonly ionic liquid-forming (IL) cations [Cat] = (2-hydroxyethyl)trimethylammonium (choline) (Chol⁺), diallyldimethylammonium (DADMA⁺), 1-ethyl-3-methylimidazolium (C₂C₁Im⁺), 1-butyl-3-methylimidazolium (C₄C₁Im⁺), 1-ethyl-3-vinylimidazolium (C₂Vim⁺), and tetrabutylphosphonium (P₄₄₄₄⁺) were synthesized. All Tb compounds exhibit strong green photoluminescence of high color purity by energy transfer from the ligand in comparison with what the analogous La compounds show, and quantum yields can reach up to 63% upon ligand excitation. When excited with an HF generator, the compounds show strong green electroluminescence with the same features of mission. The findings promise a high potential of application as emitter materials in solid-state lighting. As an additional feature, the Tb compounds show a strong response to applied external fields, rendering them multifunctional materials.

Ready Access to Anhydrous Anionic Lanthanide Acetates by Using Imidazolium Acetate Ionic Liquids as the Reaction Medium

Access to lanthanide acetate coordination compounds is challenged by the tendency of lanthanides to coordinate water and the plethora of acetate coordination modes. A straightforward, reproducible synthetic procedure by treating lanthanide chloride hydrates with defined ratios of the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([C2 mim][OAc]) has been developed. This reaction pathway leads to two isostructural crystalline anhydrous coordination complexes, the polymeric [C2 mim]n [{Ln2 (OAc)7 }n ] and the dimeric [C2 mim]2 [Ln2 (OAc)8 ], based on the ion size and the ratio of IL used. A reaction with an IL : Ln-salt ratio of 5 : 1, where Ln=Nd, Sm, and Gd, led exclusively to the polymer, whilst for the heaviest lanthanides (Dy-Lu) the dimer was observed. Reaction with Eu and Tb resulted in a mixture of both polymeric and dimeric forms. When the amount of IL and/or the size of the cation was increased, the reaction led to only the dimeric compound for all the lanthanide series. Crystallographic analyses of the resulting salts revealed three different types of metal-acetate coordination modes where η2 μκ2 is the most represented in both structure types.

Luminescent Ln-Ionic Liquids beyond Europium

Searching in the Web of Knowledge for “ionic liquids” AND “luminescence” AND “lanthanide”, around 260 entries can be found, of which a considerable number refer solely or primarily to europium (90%, ~234). Europium has been deemed the best lanthanide for luminescent applications, mainly due to its efficiency in sensitization, longest decay times, and the ability to use its luminescence spectra to probe the coordination geometry around the metal. The remaining lanthanides can also be of crucial importance due to their different colors, sensitivity, and capability as probes. In this manuscript, we intend to shed some light on the existing published work on the remaining lanthanides. In some cases, they appear in papers with europium, but frequently in a subordinate position, and in fewer cases then the main protagonist of the study. All of them will be assessed and presented in a concise manner; they will be divided into two main categories: lanthanide compounds dissolved in ionic liquids, and lanthanide-based ionic liquids. Finally, some analysis of future trends is carried out highlighting some future promising fields, such as ionogels.

Bifunctional Paramagnetic and Luminescent Clays Obtained by Incorporation of Gd3+ and Eu3+ Ions in the Saponite Framework

A novel bifunctional saponite clay incorporating gadolinium (Gd3+) and europium (Eu3+) in the inorganic framework was prepared by one-pot hydrothermal synthesis. The material exhibited interesting luminescent and paramagnetic features derived from the co-presence of the lanthanide ions in equivalent structural positions. Relaxometry and photoluminescence spectroscopy shed light on the chemical environment surrounding the metal sites, the emission properties of Eu3+, and the dynamics of interactions between Gd3+ and the inner-sphere water placed in the saponite gallery. The optical and paramagnetic properties of this solid make it an attractive nanoplatform for bimodal diagnostic applications.

Multistimuli-Responsive Lanthanide-Containing Smart Luminescent Hydrogel Actuator

Stimuli-responsive hydrogels are flourishing; however, a multiresponsive luminescent hydrogel actuator in which the stimuli do not interfere with each other is still difficult to produce. Here, a smart luminescent bilayer hydrogel actuator with shape memory and reversible luminescence switch behaviors under the co-stimulation of pH and heating is reported. Under alkaline condition, chitosan-containing layer generates physical microcrystals to fix the temporary shape of the actuator while lanthanide emits bright luminescence. Upon acid treatment, the actuator recovers to its original shape and the luminescence is quenched since the "antenna effect" between organic ligand and lanthanide ions is disrupted. It is to be noticed that this multiresponsive cycle can be repeated several times without interfering each other. This work is expected to have potential application prospects in the fields of biomimetic soft robots, sensors, and camouflage.

Bifunctional Europium(III) and Niobium(V)-Containing Saponite Clays for the Simultaneous Optical Detection and Catalytic Oxidative Abatement of Blister Chemical Warfare Agents

For the first time, the co-presence in the saponite structure of luminescent Eu^III and catalytic Nb^V metal sites was exploited for the simultaneous detection and catalytic abatement of sulfur-containing blister chemical warfare agents. Metal centers were introduced in structural positions of the saponite (in the interlayer space or inside the inorganic framework) following two different synthetic methodologies. The functionalized saponites were able to reveal the presence of a sulfur mustard simulant (2-chloroethyl)ethyl sulfide (CEES) after few seconds of contact time and more than 80 % of the substrate was catalytically decomposed after 24 h in the presence of aqueous hydrogen peroxide.

Speciation of Ionic Uranyl-Containing Complexes in in Situ Formed Dicyanonitrosomethanide-Based Ionic Liquids

A series of ionic uranyl-containing complexes, namely [C₂mim]₂[UO₂(ccnm)₄] (1), [C₄mim]₂[UO₂(ccnm)₄] (2), [N₁₁₁₁]₂[UO₂(ccnm)₄][H₂O]₂ (3), and [P₂₄₄₄]₂[UO₂(dcnm)₂(ccnm)₂] (4) [(ccnm)^- = carbamoylcyanonitrosomethanide; dcnm = dicyanonitrosomethanide; (C₂mim)⁺ = 1-ethyl-3-methylimidazolium; (C₄mim)⁺ = 1-butyl-3-methylimidazolium; (N₁₁₁₁)⁺ = tetramethylammonium; (P₂₄₄₄)⁺ = tributyl(ethyl)phosphonium)], were isolated from in situ formed dcnm-based ionic liquids and characterized systematically. It was found that the dcnm anions transformed into ccnm anions during the reactions. These anions coordinate with the uranyl cations in chelate or terminal monodentate coordination mode, affording negative divalent complex anions which can combine with different organic cations and form ionic uranyl-containing complexes. Plenty of C-H···O, N-H···O, C-H···N, N-H···N, and H···H weak interactions are formed in the crystal structures. The transformation of cyano to amide groups contributes to the crystallinity and leads to higher melting points as well as the luminescence quenching of these compounds.

Co-cross-linked lanthanide-containing nanocomposite luminescent hydrogels

We report a hydrogel with co-cross-linked networks synthesized via in situ polymerization of NIPA, LAPONITE® and lanthanide complex, endowing the hydrogel with thermoresponsive mechanical and luminescent performance.

Developing design tools for introducing and tuning structural order in ionic liquids

Ionic liquids – ionic crystals – ionic liquid crystals? Structural order in imidazolium-based ILs, a series of asymmetrical 1-dodecyl-2-methyl-3-alkylimidazolium bromides, [C₁₂C₁C_nim][Br] with n = 0–12.

Bright Solvent-Free Luminescent Liquid with Magnetism Composed of a Thiocyanate Complex of Ce(III)

Ionic liquids composed of a thiocyanate complex of Ce(III) exhibit bright cyan photoluminescence with a quantum yield close to 40% in addition to paramagnetism. The morphology of a droplet of ionic liquid changes in response to solvent vapor as a stimulus. The emission lifetime and thermal property are characterized. The Weiss temperature is evaluated from the magnetic property measurements, which indicates that antiferromagnetic exchange interaction exists between Ce(III) ions. Insight into the characteristics of the electronic transitions in the Ce(III) complex is obtained using quantum chemical calculations. Thiocyanate complexes of Ce(III) are demonstrated as promising building blocks to produce solvent-free luminescent functional materials.

Novel light-emitting clays with structural Tb3+ and Eu3+ for chromate anion detection

Tb3+ and Eu3+ ions were encapsulated for the first time in the inorganic layers of a synthetic saponite clay following a one-pot synthetic approach. The co-presence of the two metal ions led to tuneable light-emitting properties, promoted by an efficient Tb3+ → Eu3+ energy transfer and enhanced Stokes shift character. To our knowledge, the so-prepared luminescent material was tested for the first time as an optical sensor for the detection of chromate anions in water.

Luminescent ionic liquid formed from a melted rhenium(v) cluster

Recently, non-crystalline coordination materials have been shown to represent a versatile class of functional materials. However, such materials incorporating metal complex clusters have remained largely unexplored. Herein, we demonstrate that a luminescent tetranuclear ReV cluster melts at 489 K, with the cluster structure being maintained in the corresponding supercooled ionic liquid phase.

Structural and electronic properties of CuII, CoII, and NiII-containing chelate-based ionic liquids

Potential applications of chelate-based ionic liquids depend on the structural and electronic properties of this class of liquid materials. Due to the large size of chelated metal anions, the high number of potential interaction sites could lead to complex intermolecular interactions, but metal-based anions have many degrees of freedom, and they have great potential in the structural modification of the physical properties of ionic liquids. To explore the influence of varying the metal center of anions and the length of carbon chains of cationic species, four single crystal structures of chelate-based ionic liquids, ([C₁₀mim][M(F₆-acac)₃], M = Cu, Co, and Ni) and [C₆mim][Cu(F₆-acac)₃] were obtained. Taking these as the initial configurations, theoretical efforts were made to understand the structural and electronic properties. The hydrogen bonding energies of the primary hydrogen bonding interaction, in the range of 17.7-20.9 kJ mol^-1, follow the order of [C₁₀mim][Ni(F₆-acac)₃] < [C₁₀mim][Co(F₆-acac)₃] <[C₁₀mim][Cu(F₆-acac)₃], and [C_nmim][Cu(F₆-acac)₃] (n≠ 10) < [C₁₀mim][Cu(F₆-acac)₃], while the experimental viscosities exhibit an opposite trend. Furthermore, by NBO analysis, the more negative charge on the oxygen atoms of anions shows the stronger hydrogen bonding of imidazolium with C²H. The reliability of the theoretical method was supported by the comparison between the simulated and experimental infrared and UV/vis spectra. This work is useful in increasing the understanding of the structure-property relationship of chelate-based ionic liquids and furthering the rational design of novel ionic liquids.

Forcing Dicyanamide Coordination to f-Elements by Dissolution in Dicyanamide-Based Ionic Liquids

A robust general route to lanthanide dicyanamide (DCA^–) complexes has been developed where f-element salts are dissolved in DCA^–-based ionic liquids (ILs) directly or formed in situ, forcing coordination of these normally weakly coordinating soft N-donor anions, even in an ambient, non-moisture-excluding environment. A series of lanthanide complexes [C₂mim][Ln(DCA)₄(H₂O)₄] (C₂mim = 1-ethyl-3-methylimidazolium; Ln = La, Nd, Eu, Tb, Dy, and Yb) and [C₂mim]_3n[La(OH₂)₄(μ²-DCA)₄]_n[La(OH₂)₂(μ³-DCA)₃(μ²-DCA)₄]_2n(Cl)_4n were crystallized under a variety of conditions using this methodology and structurally characterized using single crystal X-ray diffraction. Although not all examples were isostructural, the dominant feature across the series was the presence of [Ln(DCA)₄(H₂O)₄]⁻ anionic nodes with all terminal DCA^– ligands accepting hydrogen bonds from the coordinated water molecules forming a 3D metal organic framework. To determine if any structural clues might aid in the further development of the synthetic methodology, the metal-free IL [C₁mim][DCA] (C₁mim = 1,3-dimethylimidazolium), a room-temperature solid, crystalline analogue of the reaction IL, which is liquid at room temperature, was also prepared and structurally characterized. The ready isolation of these compounds allowed us to begin an investigation of the physical properties such as the luminescence at room and low temperatures for the Eu, Tb, and Dy representatives.

Direct dissolution of lanthanide chloride hydrates in the DCA⁻ ionic liquids leads to coordination of DCA⁻ anions to Ln³⁺ under full displacement of chloride and partial displacement of water ligands leading to the formation of metal organic frameworks under ambient conditions. X-ray analyses reveal a significant influence of the hydrogen bonding and lanthanides’ size on crystallographic disorder in their crystal structures.

Highly Luminescent Ionic Liquids Based on Complex Lanthanide Saccharinates

Four strongly luminescent ionic liquids with complex lanthanide saccharinate anions, [C₄mim]₃[Eu(Sac)₆(H₂O)₂] (1), {C₄mpy}₅{[Ln(Sac)₆(H₂O)₂][Ln(Sac)₅(H₂O)₃]}{(H₂O)₂(CH₃CN)₂} (Ln = Sm for 2a; Ln = Eu for 2b), and [C₄mpy]₃[Eu(Sac)₆][CH₃CN] (3) (C₄mim = 1-butyl-3-methylimidazolium; C₄mpy = N-butyl-4-methylpyridinium; Sac = saccharinate), have been obtained by reacting the ionic liquids 1-butyl-3-methylimidazolium saccharinate, [C₄mim][Sac], and N-butyl-4-methylpyridinium saccharinate, [C₄mpy][Sac], with the respective lanthanide saccharinates. Single-crystal X-ray diffraction analyses reveal the respective lanthanide center to be six- or eight-coordinated by five or six saccharinate anions and two or three aqua ligands in the cases of 1 and 2 when lanthanide saccharinated hydrate was employed as the starting material. Coordination of water to the lanthanide can be avoided when using the anhydrous lanthanide saccharinate as shown by the structure of 3. Using a co-solvent, acetonitrile, to facilitate the reaction led to incorporation of solvent molecules into the crystal structure of the final materials (2 and 3). Differential scanning calorimetry analyses reveal that 1 is an ionic liquid whereas 2 and 3 are low-temperature molten salts. The three europium(III)-containing compounds (1, 2b, and 3) all show characteristic intense red emissions of Eu(III) upon excitation into levels of the saccharinate ligands (321 nm) or Eu(III) (393 nm). At room temperature, the decay times of 1 and 2b are all ∼0.5 ms, whereas the decay time of 3 amounts to 3.85 ms due to removal of aqua ligands in the first coordination sphere; accordingly, the quantum efficiencies of 1, 2b, and 3 were determined to be 15.9%, 22.95%, and 57.75%, respectively. The CIE chromaticity coordinates for all Eu compounds are in the red region and approach the NTSC standard CIE values when the temperature is increased. Sm(III)-containing compound 2a shows characteristic Sm(III) emission peaks. As expected, the CIE coordinates of samarium compound 2a fall in the orange-red region.

Designing a new type of magnetic ionic liquid: a strategy to improve the magnetic susceptibility

In order to improve the magnetic susceptibility, MILs were prepared by incorporating lanthanide ions in both the cation and anion.

Molecular dynamics investigation of water-exchange reactions on lanthanide ions in water/1-ethyl-3-methylimidazolium trifluoromethylsufate ([EMIm][OTf])

We report a kinetic study of the water exchange on lanthanide ions in water/[1-ethyl-3-methylimidazolium][trifluoromethylsufate] (water/[EMIm][OTf]). The results from ¹⁷O-NMR measurements show that the water-exchange rates in water/[EMIm][OTf] increase with decreasing size of the lanthanide ions. This trend for water-exchange is similar to the previously reported trend in water/1-ethyl-3-methylimidazolium ethyl sulfate (water/[EMIm][EtSO₄]) but opposite to that in water. To gain atomic-level insight into these water-exchange reactions, molecular dynamics simulations for lanthanide ions in water/[EMIm][OTf] have been performed using the atomic-multipole-optimized-energetics-for-biomolecular-application polarizable force field. Our molecular dynamics simulations reproduce the experimental water-exchange rates in terms of the trend and provide possible explanations for the observed experimental behavior. The smaller lanthanide ions in water/[EMIm][OTf] undergo faster water exchange because the smaller lanthanide ions coordinate to the first shell [OTf]^- anions more tightly, resulting in a stronger screening effect for the second-shell water. The screening effect weakens the interaction of the lanthanide ions with the second-shell water molecules, facilitating the dissociation of water from the second-shell and subsequent association of water molecules from the outer solvation shells.

Synthesis, structural characterization and luminescence properties of 1-carboxymethyl-3-ethylimidazolium chloride

A microcrystalline carboxyl-functionalized imidazolium chloride, namely 1-carboxymethyl-3-ethylimidazolium chloride, C₇H₁₁N₂O₂⁺·Cl^-, has been synthesized and characterized by elemental analysis, attenuated total reflectance Fourier transform IR spectroscopy (ATR-FT-IR), single-crystal X-ray diffraction, thermal analysis (TGA/DSC), and photoluminescence spectroscopy. In the crystal structure, cations and anions are linked by C-H...Cl and C-H...O hydrogen bonds to create a helix along the [010] direction. Adjacent helical chains are further interconnected through O-H...Cl and C-H...O hydrogen bonds to form a (10-1) layer. Finally, neighboring layers are joined together via C-H...Cl contacts to generate a three-dimensional supramolecular architecture. Thermal analyses reveal that the compound melts at 449.7 K and is stable up to 560.0 K under a dynamic air atmosphere. Photoluminescence measurements show that the compound exhibits a blue fluorescence and a green phosphorescence associated with spin-allowed (¹π←¹π*) and spin-forbidden (¹π←³π*) transitions, respectively. The average luminescence lifetime was determined to be 1.40 ns for the short-lived (¹π←¹π*) transition and 105 ms for the long-lived (¹π←³π*) transition.

Modifying bis(triflimide) ionic liquids by dissolving early transition metal carbamates

The authors report the first modification of ionic liquids with metal carbamates. A selection of homoleptic N,N-dialkylcarbamates of group 4 and 5 metals, M(O₂CNR₂)_n, were dissolved in bis(trifluoromethylsulfonyl)imide-based ionic liquids, i.e. [bmim][Tf₂N] and [P(oct)₄][Tf₂N], at 293 K. The resulting solutions were characterized by means of IR, UV and NMR spectroscopy, and the data were compared to those of the respective metal compounds. Notably, the dissolution process did not proceed with the release of any of the original carbamato ligands, thus preserving the intact coordination frame around the metal centre. The solvation process of Ti(O₂CNⁱPr₂)₄, as a model species, in [bmim][Tf₂N] was rationalized by DFT calculations. As a comparative study, solutions of NbF₅ and MCl₅ (M = Nb, Ta) in [bmim][Tf₂N] were also investigated, revealing the possible occurrence of solvent anion coordination to the metal centres.

Luminescent ionic liquids based on cyclometalated platinum(ii) complexes exhibiting thermochromic behaviour in different colour regions

Luminescent ionic liquids, based on anionic Pt(ii) complexes, were developed.