Tetrafluoroborate Anions Research Articles

Electrical Conductivity and Ionic Association in Tetraalkylammonium Ionic Liquids in Acetonitrile Solutions

A study is performed of the electrical conductivity (EC) of ionic liquids based on quaternary triethylalkylammonium salts with tetrafluoroborate and hexafluorophosphate anions in acetonitrile. Conductometric data on these compounds are analyzed. Constants Ka of the ionic association of the limiting molar electrical conductivity (λ0) and the standard Gibbs energy of association (ΔG0) in solutions are calculated using the Lee–Wheaton formula. The Stokes radii, limiting mobility, and limiting coefficients of diffusion are found for tetraalkylammonium cations.

Bis(2,6-pyrazolyl)pyridines as a New Scaffold for Coordination Polymers.

Two coordination polymers, Fe(LOBF3)(CH3COO)(CH3CN)2]n•nCH3CN and [Fe(LO-)2AgNO3BF4•CH3OH]n•1.75nCH3OH•nH2O (LO- = 3,3'-(4-(4-cyanophenyl)pyridine-2,6-diyl)bis(1-(2,6-dichlorophenyl)-1H-pyrazol-5-olate)), were obtained via a PCET-assisted process that uses the hydroxy-pyrazolyl moiety of the ligand and the iron(II) ion as sources of proton and electron, respectively. Our attempts to produce heterometallic compounds under mild conditions of reactant diffusion resulted in the first coordination polymer of 2,6-bis(pyrazol-3-yl)pyridines to retain the core N3(L)MN3(L). Under harsh solvothermal conditions, a hydrogen atom transfer to the tetrafluoroborate anion caused the transformation of the hydroxyl groups into OBF3 in the third coordination polymer of 2,6-bis(pyrazol-3-yl)pyridines. This PCET-assisted approach may be applicable to produce coordination polymers and metal-organic frameworks with the SCO-active core N3(L)MN3(L) formed by pyrazolone- and other hydroxy-pyridine-based ligands.

Cationic Rhodium(I) Tetrafluoroborate Catalyzed Intramolecular Carbofluorination of Alkenes via Acyl Fluoride C-F Bond Activation.

C-F bonds of acyl fluorides can be cleaved and added across tethered alkenes in the presence of a cationic rhodium(I) tetrafluoroborate catalyst. This 1,2-carbofluorination reaction offers a powerful method for the synthesis of tertiary alkyl fluoride derivatives with atom economy of 100%. Mechanistic studies indicate that the concerted action of a rhodium cation and a tetrafluoroborate anion is the key for the success of this catalytic cleavage and formation of C-F bonds in a controlled manner.

Cationic Rhodium(I) Tetrafluoroborate Catalyzed Intramolecular Carbofluorination of Alkenes via Acyl Fluoride C−F Bond Activation**

AbstractThe C−F bond of acyl fluorides can be cleaved and added across tethered alkenes in the presence of a cationic rhodium(I) tetrafluoroborate catalyst. This 1,2‐carbofluorination reaction offers a powerful method for the synthesis of tertiary alkyl fluoride derivatives with an atom economy of 100 %. Mechanistic studies indicate that the concerted action of a rhodium cation and a tetrafluoroborate anion is key for the success of this catalytic cleavage and formation of C−F bonds in a controlled manner.

Synthesis and characterization of amide-Functionalized analogues of glycine-betaine based ionic liquids and an exemplified use for the separation of copper(II) and cobalt(II)

ABSTRACT Novel series of amide functionalized analogues of glycine-betaine-based ionic liquids (AGB-ILs), namely, [N,N,N-tri(n-butyl)(2-aminoalkyl-2-oxoethyl)]ammonium (alkyl = n-butyl, and n-octyl) associated with tetrafluoroborate (BF4 −), hexafluorophosphate (PF6 −), bis(trifluorosulfonyl)imide (Tf2N−), dicyanamide (Dca−), 4-chlorosalicylate (ClSal−) and saccharinate (Sac−) anions have been synthesized and fully characterized by spectroscopic methods (IR, 1H and 13C NMR) and elemental analysis. The alkyl chain length of the organic cation and the chemical nature of inorganic or organic anion on physicochemical properties such as melting point, glass transition and decomposition temperatures, and viscosity have been described. To determine the sensitivity of Dca ligand to pH, the effect of the pH on the extraction properties of aqueous Cu2+ and Co2+ ions has been investigated in the pH range 1 to 5.

New room temperature ionic liquids prepared from an old phosphine: Using branching and diastereomeric mixtures to inherently benefit physical properties

First reported in 1966–1967, the compound tri(2-ethylhexyl)phosphine appears to be a hidden gem for ionic liquids. Although this compound offers many potential intriguing properties that are inherent due to its branching and diastereomeric nature, there is only a single report employing this material as an ionic liquid constituent. Through quaternization and anion exchange, a total of 24 new room temperature ionic liquids were prepared containing bromide (Br−), bis(trifluoromethanesulfonyl)imide (Tf2N−), hexafluorophosphate (PF6−), and tetrafluoroborate (BF4−) anions. In addition to the usual analytical methods, the compounds’ physical properties such as density, solubility, viscosity, and surface tension were probed to ascertain their suitability for aerospace applications. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were employed to study the thermal behavior of the materials focusing on phase transitions and degradation behavior. Remarkably, all ionic liquids prepared in this study are liquids at room temperature with relatively low viscosities and are soluble in many common organic solvents. Structure-property relationships were assessed, particularly focusing on the effect that the chain length appendage and/or anion type has on a given physical property. An updated synthetic procedure and characterization of the tri(2-ethylhexyl)phosphine starting material are provided. A new synthesis procedure for the starting material silver(I) tetrafluoroborate is also reported.

Innenrücktitelbild: Salt Metathesis: Tetrafluoroborate Anion Rapidly Fluoridates Organoboronic Acids to give Organotrifluoroborates (Angew. Chem. 16/2023)

Salt metathesis and BFX (boron–fluoride exchange) of BF4− with boronic acids generates RBF3− derivatives, thus showing the solvolytic lability of BF4− that enables its use as a fluorinating agent, even though many highly reactive reagents employ BF4− as a non-reactive counteranion. In their Research Article (e202215371), David M. Perrin and co-workers report the synthesis of RBF3− derivatives via a salt metathesis reaction using a series of MBF4 salts in methanol. This work highlights the proclivity of BF4−, generally considered weakly coordinating and unreactive, to rapidly fluorinate boronic acids.

Inside Back Cover: Salt Metathesis: Tetrafluoroborate Anion Rapidly Fluoridates Organoboronic Acids to give Organotrifluoroborates (Angew. Chem. Int. Ed. 16/2023)

Salt metathesis and BFX (boron–fluoride exchange) of BF4− with boronic acids generates RBF3 derivatives thus showing the solvolytic lability of BF4− that enables its use as a fluorinating agent, even though many highly reactive reagents employ BF4− as a non-reactive counter anion. In their Research Article (DOI: 10.1002/anie.202215371), David M. Perrin and co-workers report the synthesis of RBF3− derivatives via a salt metathesis reaction using a series of MBF4 salts in methanol. This work highlights the proclivity of BF4−, generally considered weakly coordinating and unreactive, to rapidly fluorinate boronic acids.

Salt Metathesis: Tetrafluoroborate Anion Rapidly Fluoridates Organoboronic Acids to give Organotrifluoroborates.

Tetrafluoroborate (BF4 - ) has long been used as a spectator counter anion. Herein, we report an unprecedented salt metathesis between a variety of BF4 - salts and a series of organoboronic acids yielding the corresponding organotrifluoroborates. We identified conditions for fast and efficient fluoridation (<1 h) with minimal workup. Fundamentally, this work discloses the proclivity of BF4 - to exchange fluoride atoms with organoboronates, highlighting the lability of BF4 - .

Salt Metathesis: Tetrafluoroborate Anion Rapidly Fluoridates Organoboronic Acids to give Organotrifluoroborates

AbstractTetrafluoroborate (BF4−) has long been used as a spectator counter anion. Herein, we report an unprecedented salt metathesis between a variety of BF4− salts and a series of organoboronic acids yielding the corresponding organotrifluoroborates. We identified conditions for fast and efficient fluoridation (&lt;1 h) with minimal workup. Fundamentally, this work discloses the proclivity of BF4− to exchange fluoride atoms with organoboronates, highlighting the lability of BF4−.

Synthesis of Zinc Sulfide Nanoparticles Using Pyridinium Ionic Liquids

Zinc sulfide nanoparticles (quantum dots) were synthesized from aqueous solutions of sodium sulfide and zinc sulfate using pyridinium ionic liquids. The average sizes of zinc sulfide nanoparticles were determined by UV spectroscopy, X-ray diffraction, probe and scanning electron microscopy. The influence of the structure and concentration of pyridinium ionic liquids with the tetrafluoroborate anion of the same name on the size of zinc sulfide nanoparticles has been studied. The effect of the precursor concentration on the size of the nanoparticles formed in the ash was established.

Improved Current Efficiency of Quantum Dot Light‐Emitting Diodes by Utilizing ZnO Nanoparticles and an Organic Ionic Interlayer

AbstractThe solution‐processed QLED (quantum dot light‐emitting diode) has a great potential for low‐cost and large‐scale displays. However, the solution‐processed QLED has a limitation in the current efficiency due to the rough surface of the quantum dot layer causing shunt leakage. This paper reports solution‐processed highly current‐efficient QLED utilizing zinc oxide nanoparticles (ZnO NPs) and an organic ionic interlayer as an electron injection layer. The organic ionic materials create the permanent interface dipole by shifting the vacuum energy using tetrabutylammonium (TBA) cations and tetrafluoroborate (BF4) anions under the applied electric field. The dipole effectively reduces the electronic injection barrier to provide charge carrier balance of the holes and electrons in the emissive layer. As a result, the maximum current efficiency and power efficiency for the device structure of QLEDs ITO/PEDOT : PSS/PVK/CdSe@ZnS QDs/ZnO NPs/TBABF4+PEG/Al (23.9 cd A−1 and 12.9 lm W−1) enhanced significantly compared to the structure of QLEDs ITO/PEDOT : PSS/PVK/CdSe@ZnS QDs/ZnO NPs/PEI/Al (9.7 cd A−1 and 5.8 lm W−1) and the structure of QLEDs ITO/PEDOT : PSS/PVK/CdSe@ZnS QDs/ZnO NPs/Al (6.8 cd A−1 and 4.1 lm W−1). The improvement of the current efficiency can be analyzed under the Space Charge‐Limited Current regime. In addition, this paper examines the existence of parasitic resistances including series resistance and shunt resistance by modeling the QLED device as a single exponential diode model. Finally, we can evaluate the influence of the ionic interlayer on the entire QLED device in reducing the leakage current and the current‐voltage (I–V) characteristic of the fabricated QLED devices. We believe the presented high‐performance quantum dot light‐emitting diodes have a high potential and impact on lighting and display technologies.

Structural Investigation of the Anion Effect in Ruthenium(II) Arene Complexes Bearing Pyridyl-Triazole Ligands: Implications for Transfer Hydrogenation Catalysis

Cationic ruthenium(II) half-sandwich complexes bearing 1-octyl-4-pyridyl-1H-1,2,3-triazole ligands were found to display strong ion-pairing, the strength of which was dependent on the nature of the anionic counterion. A detailed spectroscopic analysis revealed that the ion-pairing process is also solvent-dependent. For the complex containing the 1-octyl-4-pyridyl-1H-1,2,3-triazole ligand and a tetraphenylborate counterion (1a), the spectral data reveal that the complex forms a collection of four ions (quadruple ions) in CHCl3. In contrast, one set of contact ion-pairs (CIPs) was observed in MeCN with the extent of ion-pairing being 88%. Analogous complexes in which the tetraphenylborate counterion is replaced by a hexafluorophosphate (2a) and tetrafluoroborate (3a) anion exist as CIPs (92 and 90%) and solvent-separated ion-pairs (55 and 56%) in CHCl3 and MeCN, respectively. Conductivity measurement results indicate that the extent of ion-pairing for 1a, 2a, and 3a in 2-PrOH is greater in comparison to the CIPs formed in CH2Cl2. Our results provide a rationale for the reactivity differences observed for 1a and 2a in transfer hydrogenation catalysis.

Importance of Anion–Anion Pairing for Capacitance of Carbon/Ionic Liquid Interfaces

The capacitance of carbon electrodes can be enhanced by tuning nanoscale roughness of the electrode surface, which facilitates separation between cations and anions within the electrical double layer. As the extent of ion separation depends on the ion correlation of bulk electrolytes, it is expected that the intrinsic electrical properties of ionic liquids (ILs) will also influence the double-layer structure and capacitance at nanostructured electrode interfaces. In this work, we use constant voltage molecular dynamics simulations to investigate the differential capacitance profiles for three different ionic liquids at model graphene electrode with subnanometer scale surface roughness. We focus on the ionic liquids composed of 1-butyl-3-methylimidazolium (BMIm+) cations and bistriflimide (TFSI–), triflate (OTf–), or tetrafluoroborate (BF4–) anions. Surprisingly, we find that [BMIm+][TFSI–] exhibits significantly enhanced differential capacitance at high positive potential compared to [BMIm+][BF4–] and [BMIm+][OTf–] with smaller anions. We demonstrate that this unexpected capacitance trend is due to nonpolar interactions between trifluoromethyl groups of TFSI– anions that promote TFSI–/TFSI– pairing at the electrode interface. These anion pairs lead to significantly reduced BMIm+ density in the [BMIm+][TFSI–] double layer compared to the other two ionic liquids. By contrast, no anion pairing occurs for [BMIm+][BF4–] and [BMIm+][OTf–] at the same voltage regime, so nonpolar alkyl groups of BMIm+ cations still predominantly accumulate at the nanostructured electrode interface, resulting in only slight enhancement of capacitance due to the surface roughness effect. This physical insight is important for controlling IL interfacial structure to enhance the capacitance of nanostructured electrodes.

Quantitative insights into noncovalent interactions involving halogen and tetrel bonds in 2,4,6-trimethylpyrylium tetrafluoroborate.

The crystal and molecular structure of an organic salt, in which a 2,4,6-trimethylpyrylium cation forms a salt with a tetrafluoroborate anion, namely, 2,4,6-trimethylpyrylium tetrafluoroborate, C8H11O+·BF4-, has been experimentally realized. The compound crystallizes in the orthorhombic centrosymmetric space group Pnma. The crystal packing is stabilized via a subtle interplay of [F3-B-F]-...O+-C fluorine/oxygen-centred halogen/chalcogen bonds and Cδ+...Fδ- tetrel-bonded contacts. Although the O centre has a formal charge of +1, the estimation of the partial negative charges on O is in accordance with electronegativity considerations. Hirshfeld surface analysis, which also includes an analysis of the three-dimensional deformation density, along with molecular electrostatic potential (MESP) calculations, provides quantitative insights into the nature of the intermolecular interactions. The topological analysis of the electron-density distribution has been performed using AIMAll and TOPOND, and unequivocally establishes the bonding character associated with the different noncovalent interactions. In addition, NBO analysis and polarizability calculations using PolaBer render deeper physical insights into the electronic characteristics of these noncovalent interactions.

Interplay of Local Dynamic Heterogeneity, Mesoscale Aggregate Dynamics, and Transport Properties of Imidazolium Ionic Liquids

Ion dynamics and charge transport in 1-methyl-3-octylimidazolium ionic liquids with chloride, bromide, tetrafluoroborate, tricyanomethanide, hexafluorophosphate, triflate, tetrachlorodialuminate, bis(trifluoromethylsulfonyl)imide, and heptachlorodialuminate anions are investigated by broadband dielectric spectroscopy, rheology and viscometry. A detailed analysis reveals anion and temperature-dependent separation of characteristic relaxation rates extracted from various representations of the dielectric spectra. The degree of separation is interpreted as an experimental signature of significant heterogeneity of the local ion dynamics associated with the structural glass transition, viscosity, and dc ion conductivity. It is found that the degree of dynamic heterogeneity correlates closely with the strengths of slow dielectric and mechanical relaxations previously attributed to the dynamics of mesoscale solvophobic aggregates. Increasing local dynamic heterogeneity correlates with an increase in the strength of the slow, aggregate dielectric relaxation and a decrease in the strength of the slow, aggregate mechanical relaxation. Accordingly, the local dynamic heterogeneity correlates with an increase in the static dielectric permittivities and a decrease in the contribution of aggregate dynamics to the zero-shear viscosities. These results are presented within a broader framework of current understanding of dynamics in ionic liquids and the interplay of dynamics, solvophobic aggregation, and charge transport in these technologically important systems.

Pseudo-halide anion engineering for efficient quasi-2D Ruddlesden-Popper tin perovskite solar cells

Quasi-two-dimensional (2D) organic-inorganic hybrid tin perovskites have emerged as promising alternatives to lead-based perovskites in thin-film photovoltaics because of their reduced toxicity and improved stability. However, the undesired small n-value 2D phases and disordered crystal orientation enormously restrict the efficiency of quasi-2D tin perovskite solar cells (PSCs) due to uncontrollable nucleation and crystal growth processes. Here, we propose a mixed pseudo-halide anion engineering approach by using acetate (Ac − ) and tetrafluoroborate (BF 4 − ) anions to make quasi-2D Ruddlesden-Popper perovskites with a target formula of PEA 2 FA 4 Sn 5 I 16 . We find that the mixed Ac − and BF 4 − anions can not only promote homogeneously distributed PEA + cations in the precursor by effectively breaking the PEA + ···PEA + stacking but also retard the crystallization process by coordinating with unbonded SnI 2 , thereby, significantly reducing small n-value 2D phases, improving the crystal orientation, and suppressing the Sn 2+ oxidation. The resulting PSC exhibits up to 9% power conversion efficiency and 400 h stability. • Efficiency up to 9% is achieved for 2D tin perovskite solar cells with good stability • The crystallization process is successfully controlled by pseudo-halide engineering • Vertical orientation and reduced small n-value 2D phases are achieved The poor stability of tin perovskites greatly hinders their photovoltaic applications. Li et al. propose a pseudo-halide engineering strategy to grow 2D Ruddlesden-Popper tin perovskites with reduced small n-value 2D phases and improved crystal orientation. Efficiency up to 9% and 400 h stability is achieved.

Hierarchical intercalation of tetrafluoroborate anion into graphite electrode from sulfolane

The anion storage behavior of graphite positive electrode in a dual-ion battery is closely related to the solvation of anion in the corresponding electrolyte solution. The classical electrolyte solutions of LiBF4-sulfolane (SL) have long been recognized in the community of lithium batteries and still appear promising in dual-ion batteries. Nevertheless, the solvation of BF4− by SL has seldom been addressed before. In this study, the solvation states of SL-BF4− are adjusted by varying LiBF4 concentration or introducing auxiliary salts of LiPF6 or SBPBF4 (SBP: spiro-(1,1′)-bipyrrolidinium) in the electrolyte solutions of Li/graphite dual-ion cells. The electrochemical storage processes of SL-BF4− anions in graphite electrodes are investigated through in situ X-ray diffraction measurements. Two kinds of graphite intercalation compounds (GICs) with contrastive intercalation gallery heights (IGHs) have been discovered, which are ascribed to the storage of different kinds of SL-BF4− anions in graphite electrode. The interactions between ions and SL in the electrolyte solutions are characterized by Fourier transform infrared spectroscopy and then correlated with the performance of Li/graphite cells.

Simple but effective: Liquid superlubricity with high load capacity achieved by ionic liquids

Macroscale superlubricity is a new field that can greatly reduce energy consumption due to friction, which accounts for approximately 30% of human nonrenewable energy. However, prior research on liquid superlubricity mostly involved low contact pressures (<600 MPa). Here, we evaluated the lubrication and adsorption properties of ionic liquid alcohol solutions (ILs(as)) with different alkyl chain lengths and monovalent anions between Si3N4 and sapphire surfaces. Robust macroscale superlubricity and ultrahigh load capacity exceeding 1 GPa were obtained by protective adsorption layer caused by tribochemical reactions. Zeta potential measurements and simulation analysis revealed that the ceramic interfaces were enriched with numerous ionic liquid (IL) anions, preventing the direct collision of the asperities of the friction pairs. The relatively low sliding energy barrier and extremely strong electrostatic repulsion developed between these asperities enhanced the superlubricity and ultrahigh load capacity. Meanwhile, long alkyl chains and tetrafluoroborate anions more easily met the hydrodynamic boundary conditions at the solid–liquid interface, and the formation of low energy consumption channels through the smooth potential energy fluctuation surface generated extremely low shear stress. Such macroscale lubrication provides a novel method of achieving extremely high contact pressure in ILs(as), which could enable liquid superlubricity in practical industrial applications.

Interfacial Electrochemistry-Induced Detachable Adhesives with Ultra-High Bonding Strength and Detaching Efficiency.

Detachable adhesives with simultaneously high bonding strength and detaching efficiency have remained a great challenge in adhesion science. The existing detachable adhesives (e.g., solid-liquid phase transitions-based adhesives) usually show low initial cohesion and require long detaching time (several minutes or hours for transitions). Herein, by introducing ionic liquids (ILs) and soft polyethylene glycol (PEG) into a rigid epoxy precursor and curing, we demonstrated the adhesives with both high initial bonding strength (>13 MPa) and detaching efficiency (100% detachment within 10 s under a 90 V DC voltage). The high initial bonding strength is due to the imidazolium cations of ILs and their ion-dipole interactions with PEG can promote the curing of epoxy, decrease the glass-transition temperature, increase the interfacial wettability, and transmit external stress. Also, the outstanding detaching efficiency is because the tetrafluoroborate anions of ILs can electrochemically react rapidly under a voltage and generate fluorinated nanoparticles at the bonding interface within 1 minute. The high bonding and electrochemistry-induced detaching mechanism were further characterized. This work opens up a new avenue for the rational design of fast-detachable adhesives with high bonding strength, showing wide potential in many modern fields.