Anion Pair Research Articles

Structural Insight on Supramolecular Polyion Salts: Inositol Hexaphosphate Enclosed in Cationic Macrocyclic Clusters.

Supramolecular macrocyclic forces have been used to trap phytate, myo-inositol-1,2,3,4,5,6-hexakisphosphate, a key bioanion with multiple roles in metabolic processes. Due to the complex chemistry of six multivalent phosphates surrounding the small, cyclic inositol framework, crystallographic information of simple phytate salts has been elusive. This report represents a combined crystallographic, theoretical, and solution binding investigation of a supramolecular macrocyclic complex of phytate. Together, the results provide significant insight to phytate's intramolecular and intermolecular interactions at the microenvironment level. The macrocycle-phytate aggregates consist of phytate anionic pairs, each partly sandwiched by two 24-membered, amide/amine-based cationic macrocycles. The phytate ion pairs hold the tetrameric macrocyclic array together by six strong intermolecular hydrogen bonds. Both phytates crystallize in 1a5e phosphate conformations (one axial (P2) and five equatorial phosphates). Solution NMR binding studies in 1 : 1 DMSO-d6 : D2 O indicate 2 : 1 macrocycle:phytate associations, suggesting that the sandwich-like nature of the complex holds together in solution. DFT studies indicate the likely occurrence of dynamic intramolecular interchange of phosphate protons, as well as important roles for the axial (P2) phosphate in both intramolecular and intermolecular hydrogen bonding interactions.

Effects of non-specific and specific solvation on structure of tripropylammonium-based protic ionic liquids: Insight from computational modeling

To explore the structure of three protic ionic liquids based on tripropylammonium cation and anions of strong acids – methanesulfonic, sulfuric, and triflic acids – we employed different computational methods, including quantum chemical calculations and molecular dynamics simulations. Solvation effects (non-specific and specific) were considered in order to evaluate the applicability of the methods used for the description of the ionic liquid’s structure. In each of the ionic liquids, we identified the cation–anion pair where a strong hydrogen bond and coulombic interactions kept the ions together. The results of both gas phase and implicit solvation calculations show an increase in the strength of the hydrogen bond and the magnitude of the ion-ion interaction energy in the ion pairs with tripropylammonium cation in the order of anions: triflate < hydrogen sulfate < mesylate, but the absolute values become smaller when going from the gas phase to the continuum medium. The molecular dynamics simulations reveal that the cation–anion pairs are preserved in the bulk phase of these liquids, but besides this, the formation of hydrogen bonds between anions in the tripropylammonium hydrogen sulfate is also possible.

Synthesis and crystal structure of structurally different cadmium selenocyanate and thiocyanate coordination compounds containing 3‐chloropyridine as ligand

AbstractFour compounds with the composition Cd(NCSe)2(3‐ClPy)4 (1), [Cd(NCSe)2(3‐ClPy)2] ⋅ 3‐ClPy (2), Cd(NCSe)2(3‐ClPy)2 (3) and Cd(NCSe)2(3‐ClPy) (4) with 3‐ClPy = 3‐chloropyridine were synthesized. In the structure of 1 discrete complexes are observed, whereas in 2 the Cd cations are linked by pairs of selenocyanato anions into chains and between the chains 3‐chloropyridine solvate molecules are embedded. In compound 3 each two Cd cations are linked by pairs of anionic ligands into dinuclear units, that are further connected into layers by μ‐1,3 single bridging selenocyanate anions. In compound 4, both, octahedrally and tetrahe‐ drally coordinated Cd cations are present, that are linked by μ‐1,3‐ bridging anionic ligands into a three‐.dimensional network.Thermoanalytical investigations prove that compound 1 loses the 3‐chloropyridine ligands stepwise upon heating and transforms into compound 4 via compound 3 as an intermediate. Further investigations show that the thiocyanate analogue Cd(NCS)2(3‐ClPy) 5 that is not reported in the literature can also be prepared. Since no single crystals were available, the structure was solved from PXRD data and refined using the Rietveld method, which revealed that this compound is an isomer of 4. In its crystal structure the Cd cations are linked by μ‐1,3(N,S) and μ‐1,3,3(N,S,S)‐bridging anionic ligands into chains that are further connected via Cd2S2 rings into double chains.

Ultra-Low Viscosity and High Magnetic Susceptibility Magnetic Ionic Liquids Featuring Functionalized Diglycolic Acid Ester Rare-Earth and Transition Metal Chelates.

Magnetic ionic liquids (MILs) comprise a subcategory of ionic liquids (ILs) and contain a paramagnetic metal center allowing them to be readily manipulated by an external magnetic field. While MILs are popularly employed as solvents in catalysis, separations, and organic synthesis, most low viscosity combinations possess a hydrophilic character that limits their use in aqueous matrices. To date, no study has reported the synthesis and characterization of hydrophobic MILs with viscosities similar to those of hydrophilic MILs and organic solvents while simultaneously exhibiting enhanced magnetic and thermal properties. In this study, diglycolic acid esters are employed as ligands to chelate with paramagnetic metals to produce cations that are paired with metal chelates composed of hexafluoroacetylacetonate ligands to form MILs incorporating multiple metal centers in the cation and anion. Viscosity values below 31.6 cP were obtained for these solvents, the lowest ever reported for hydrophobic MILs. Solubilities in nonpolar solvents such as benzene were observed to be as high as 50% (w/v) MIL-to-solvent ratio while being insoluble in water at concentrations as low as 0.01% (w/v). Effective paramagnetic moment values for these solvents ranged from 5.33 to 15.56 Bohr magnetons (μB), with mixed metal MILs containing multiple lanthanides in the anion generally offering higher magnetic susceptibilities. MILs composed of ligands containing octyl substituents were found to possess thermal stabilities up to 190 °C. The synthetic strategies explored in this study exploit the highly tunable nature of the employed cation and anion pairs to design versatile ultra-low viscosity magnetoactive solvents that possess tremendous potential and applicability in liquid-liquid separation systems, catalysis, and microfluidics where the mechanical movement of the solvent can be easily facilitated using electromagnets.

Water binding and hygroscopicity in π-conjugated polyelectrolytes

The presence of water strongly influences structure, dynamics and properties of ion-containing soft matter. Yet, the hydration of such matter is not well understood. Here, we show through a large study of monovalent π-conjugated polyelectrolytes that their reversible hydration, up to several water molecules per ion pair, occurs chiefly at the interface between the ion clusters and the hydrophobic matrix without disrupting ion packing. This establishes the appropriate model to be surface hydration, not the often-assumed internal hydration of the ion clusters. Through detailed analysis of desorption energies and O–H vibrational frequencies, together with OPLS4 and DFT calculations, we have elucidated key binding motifs of the sorbed water. Type-I water, which desorbs below 50 °C, corresponds to hydrogen-bonded water clusters constituting secondary hydration. Type-II water, which typically desorbs over 50–150 °C, corresponds to water bound to the anion under the influence of a proximal cation, or to a cation‒anion pair, at the cluster surface. This constitutes primary hydration. Type-III water, which irreversibly desorbs beyond 150 °C, corresponds to water kinetically trapped between ions. Its amount varies strongly with processing and heat treatment. As a consequence, hygroscopicity—which is the water sorption capacity per ion pair—depends not only on the ions, but also their cluster morphology.

Theoretical Study on the Mechanism of Cobalt-Catalyzed C-O Silylation and Stannylation.

Organosilicon and organotin compounds have been widely used in many fields, such as organic synthesis, materials science, and biochemistry, because of their unique physical and electronic properties. Recently, two novel compounds containing C-Si or C-Sn bonds have been synthesized. These compounds can be used for late modification of drug-like molecules such as probenecid, duloxetine, and fluoxetine derivatives. However, the detailed reaction mechanisms and the influencing factors that determine selectivity are still unclear. Moreover, several questions remain that are valuable to investigate further, such as (1) the influence of the solvent and the lithium salt on the reaction of the Si/Sn-Zn reagent, (2) the stereoselective functionalization of C-O bonds, and (3) the differences between silylation and stannylation. In the current study, we have explored the above issues with density functional theory and have found that stereoselectivity was most likely caused by the oxidative addition of cobalt to the C-O bond of alkenyl acetate with chelation assistance and that transmetalation was most likely the rate-determining step. For Sn-Zn reagents, the transmetalation was achieved by anion and cation pairs, whereas for Si-Zn reagents, the process was facilitated by Co-Zn complexes.

Weakening the Interchain Interactions in One Dimensional Cobalt(II) Coordination Polymers by Preventing Intermolecular Hydrogen Bonding.

The reaction of Co(NCS)2 with N-methylaniline leads to the formation of [Co(NCS)2(N-methylaniline)2]n (1), in which the cobalt(II) cations are octahedrally coordinated and linked into linear chains by pairs of thiocyanate anions. In contrast to [Co(NCS)2(aniline)2]n (2) reported recently, in which the Co(NCS)2 chains are linked by strong interchain N-H···S hydrogen bonding, such interactions are absent in 1. Computational studies reveal that the cobalt(II) ions in compound 1 show an easy-axis anisotropy that is lower than in 2, but with the direction of the easy axis being similar in both compounds. The high magnetic anisotropy is also confirmed by magnetic and FD-FT THz-EPR spectroscopy, which yield a consistent gz value. These investigations prove that the intrachain interactions in 1 are slightly higher than in 2. Magnetic measurements reveal that the critical temperature for magnetic ordering in 1 is significantly lower than in 2, which indicates that the elimination of the hydrogen bonds leads to a weakening of the interchain interactions. This is finally proven by FD-FT THz-EPR experiments, which show that the interchain interaction energy in the N-methylaniline compound 1 is nine-fold smaller than in the aniline compound 2.

Exchange Interactions and Magnetic Properties of a Molecular Mn18-Ring Complex.

[Mn3O(OAc)7(HOAc)]6·xAcOH (x = 6-9) represents a rare example of a compound containing molecular Mn18-rings. These are formed by Mn3(µ3-O) subunits in which the high-spin Mn(III) centers are bridged by three pairs of acetate anions (AcO-). An AcOH molecule coordinates to one of the Mn atoms leading to [Mn3(µ3-O)(µ2-OAc)6(AcOH)]-units, designated in short as Mn3-units, that are interconnected by acetate anions via the other two Mn atoms to form Mn18-rings. Magnetic measurements show weak ferromagnetic interactions between them that are suppressed in strong magnetic field. Quantum-chemical calculations on Mn3 model complexes using independently DFT and ab-initio multi reference methods (CASSCF/NEVPT2) show a correlation between the orientation of the pseudo-Jahn-Teller axes of pairs of Mn(III) magnetic centers and corresponding exchange coupling energies. Weak coupling between Mn3-units within the Mn18-ring allowed to simulate the magnetic susceptibility vs temperature dependence in terms of basically uncoupled magnetic moments of each Mn3-unit within the ring.

Room-temperature ionic liquids as candidate materials for produced water desalination: Experiments and molecular dynamic analysis

Room-temperature ionic liquids (RTILs) have been promoted as “green” chemicals that can be used as alternatives to conventional volatile organic solvents. In addition to low volatilities, hydrophobicity for organic liquids and hydrophilicity for ions in RTILs lead to a wide spectrum of applications. ILs have recently been considered as alternative solvents to carboxylic acids and amines used for solvent extraction desalination (SED). RTILs are used in pairs of cations and anions that can significantly influence SED potentials. This study aimed to find an optimal combination of cationic and anionic RTIL as a desalination solvent through theoretical, experimental, and computational approaches. SED potentials in terms of water absorption and salt rejection were investigated for ten pairs of RTILs using different combinations of imidazolium and phosphonium cations with various anions. SED potentials were highly dependent on the anion type, with Tf2N showing the most promising SED potential. Imidazolium based RTILs exhibited better SED performances than phosphonium based RTILs in experiments. [BMIM][Tf2N] was recommended as a candidate SED-IL material, showing a water absorption and salt rejection of 1.73 % and 93.7 %, respectively. Molecular dynamics (MDs) simulation was implemented in parallel in order to examine and analyze intermolecular interactions that led to particular experimental observations.

Synthesis, crystal structures, thermal and magnetic properties of Mn(NCS)2 coordination compounds with 3-cyanopyridine

The reaction of Mn(NCS)2 and 3-cyanopyridine in different solvents leads to the formation of pure Mn(NCS)2(3-cyanopyridine)4 (1), Mn(NCS)2(3-cyanopyridine)2(H2O)2-bis(3-cyanopyridine) solvate (2) and Mn(NCS)2(3-cyanopyridine)(H2O) (4). In further investigations single crystals of Mn(NCS)2(3-cyanopyridine)2(H2O)2 (3) were accidentally obtained, but this compound cannot be prepared pure. Compounds 1-3 consist of discrete complexes with octahedrally coordinated Mn cations, whereas in compound 4 the Mn cations are linked by single µ-1,3-bridging thiocyanate anions into chains, that are further connected into layers by the 3-cyanopyridine coligands. Thermogravimetric measurements reveal that upon heating compound 1 loses some of the 3-cyanopyridine ligands and transforms into [(Mn(NCS)2)3(3-cyanopyridine)4]n (5), which is isotypic to the corresponding Cd compound reported in the literature. In this structure, the Mn cations are linked by pairs of thiocyanate anions into chains that are further connected into layers by every second 3-cyanopyridine coligand. When compound 2 is heated, a transformation into the complex 1 is observed, that upon further heating transforms into 5. Magnetic measurements for compound 4 show that the Mn-NCS-Mn exchange is dominant and antiferromagnetic, and susceptibility dependence in the paramagnetic phase is well described by the Heisenberg spin chain model. Below 2.77 K, the Mn(II) spins in 4 are ordered with a weak ferromagnetic component due to the Dzyaloshinskii-Moriya interaction.

CO2 Adsorption Based on Porphyrin Based Porous Organic Polymers

In order to efficiently catalyze the cycloaddition reaction of CO2 and epoxy alkanes under mild environment and no catalyst, this paper designed and synthesized two kinds of porphyrin based porous organic polymers—porphyrin based porous organic polymer containing carboxyl group (ppop-cooh) and porphyrin based porous organic polymer containing quaternary ammonium salt ion pair. Quaternary ammonium salt cation anion pair nucleophilic groups and metal active centers were introduced into the polymer by pre- and post-modification respectively. The chemical structure and pore structure of the polymer were characterized by infrared spectroscopy and physical adsorption instrument, and its effect as a catalyst on the cycloaddition reaction of CO2 and epoxy alkanes was studied. From the results, it is demonstrated that the two polymers had a multistage pore structure with a specific surface area of 302 m2/g-514 m2/g. The synergistic effect of Lewis acid metal ions, nucleophiles and multistage pore structure in the polymer significantly promotes the cycloaddition reaction between CO2 and epoxy alkanes. Under mild conditions (80°C, 0.3 MPa, 24h), the selectivity and conversion of the reaction reach more than 99%. The polymer is repeated for many times. After use, it still has good catalytic performance.

Ligand-Promoted Bifunctional Cobalt-Catalyzed Carbonylation-Polymerization of Epoxides: One Step to Polyhydroxyalkanoates

Poly(3-hydroxyalkanoates) (PHAs) are an important category of biodegradable plastics with properties similar to those of conventional ones. The development of a simple and efficient catalytic system for PHAs from the most abundant chemicals is economically important. Now we report an in situ generated bifunctional cobalt-catalyzed direct carbonylation-polymerization of epoxides in high efficiency in the presence of a diphosphine oxide ligand WenPhos oxide, which can be easily made from diphenyl sulfone in three steps with regular reagents. In addition, this ligand can promote the disproportionation of Co2(CO)8 to [Co(CO)4]− and Co(II) which is coordinated with phosphine oxide and sulfone oxide. Mechanistic studies indicate that this reaction is not from the ring-opening polymerization of in situ generated β-lactone. Instead, the phosphine oxide coordinated cobalt cation and [Co(CO)4]− anion pair catalyzed direct carbonylation-polymerization of epoxide was proposed based on previous studies, some control experiments, and X-ray structures of the cobalt complexes.

Syntheses and crystal structures of bis-(4-methyl-pyridine-κN)bis-(seleno-cyanato-κN)zinc(II) and catena-poly[[bis-(4-methyl-pyridine-κN)cadmium(II)]-di-μ-seleno-cyanato-κ2 N:Se;κ2 Se:N

The reactions of Zn(NO3)2 .6H2O and Cd(NO3)2 .4H2O with KSeCN and 4-meth-yl-pyridine (C6H7N; 4-picoline) lead to the formation of crystals of bis-(4-methyl-pyridine-κN)bis-(seleno-cyanato-κN)zinc(II), [Cd(NCSe)2(C6H7N)2] (1), and catena-poly[[bis-(4-methyl-pyridine-κN)cadmium(II)]-di-μ-seleno-cyanato-κ2 N:Se;κ2 Se:N], [Cd(NCSe)2(C6H7N)2] n (2), suitable for single-crystal X-ray diffraction. The asymmetric unit of compound 1 consists of one Zn cation that is located on a twofold rotation axis as well as one seleno-cyanate anion and one 4-methyl-pyridine ligand in general positions. The Zn cations are tetra-hedrally coordinated by two terminal N-bonding thio-cyanate anions and two 4-methyl-pyridine ligands, forming discrete complexes. The asymmetric unit of compound 2 consists of two crystallographically independent Cd cations, of which one is located on a twofold rotation axis and the second on a center of inversion, as well as two crystallographically independent seleno-cyanate anions and two crystallographically independent 4-methyl-pyridine ligands in general positions. The Cd cations are octa-hedrally coordinated by two N- and two S-bonding seleno-cyanate anions and two 4-methyl-pyridine ligands and are linked into chains by pairs of seleno-cyanate anions. Within the chains, the Cd cations show an alternating cis-cis-trans and all-trans coordination and therefore, the chains are corrugated. PXRD investigations prove that the Zn compound was obtained as a pure phase and that the Cd compound contains a very small amount of an additional and unknown phase. In the IR spectrum of 1, the CN stretching vibration of the seleno-cyanate anion is observed at 2072 cm-1, whereas in the 2 it is shifted to 2094 cm-1, in agreement with the crystal structures.

Cation functional group effect on SO2 absorption in amino acid ionic liquids.

Introduction: The effect of the functional group of the cation on SO2 acidic gas absorption by some designed amino acid ionic liquids (AAILs) was studied. Methods: An isolated pair of glycinate anion and pristine imidazolium-based cation, as well as decorated cation functionalized by hydroxyl (OH), amine (NH2), carboxylic acid (COOH), methoxy (OCH3), and acetate (CH3COO) groups, were structurally optimized by density functional theory (DFT) using split-valence triple-zeta Pople basis set. Results and Discussion: The binding and Gibbs free energy (ΔGint) values of SO2 absorption show the AAIL functionalized by the COOH group is the most thermodynamically favorable green solvent and this functional group experiences the closest distance between anion and captured SO2 and vice versa in the case of cation … SO2 which may be the main reason for being the best absorbent; in addition, the highest net charge-transfer amount of SO2 is observed. Comparing the non-covalent interaction of the systems demonstrates that the strongest hydrogen bond between captured gas and anion, as well as π-hole, and van der Waals (vdW) interaction play critical roles in gas absorption; besides, the COOH functional group decreases the steric effect while the CH3COO functional group significantly increases steric effect after absorption that declines the hydrogen bond.

Symmetry-breaking charge separation in weakly coupled anthracene dimers

The charge separation (CS) and charge recombination (CR) of the symmetry-breaking charge-separation process is optimized via molecular engineering. An unprecedently high value (∼2500) of the ratio of the rates of CS over CR is achieved.

Syntheses, crystal structures and Hirshfeld surface analysis of 4-(4-nitro-phen-yl)piperazin-1-ium tri-fluoro-acetate and 4-(4-nitro-phen-yl)piperazin-1-ium tri-chloro-acetate.

The synthesis and crystal structures of the mol-ecular salts of 4-(4-nitro-phen-yl)piperazine with tri-fluoro-acetate, namely, 4-(4-nitro-phen-yl)piperazin-1-ium tri-fluoro-acetate, C10H14N3O2 +·C2F3O2 - (I), and with tri-chloro-acetate, namely, 4-(4-nitro-phen-yl)piperazin-1-ium tri-chloro-acetate, C10H14N3O2 +·C2Cl3O2 -, (II), are reported and compared. A partial positional disorder of the anions was found. In both structures, the piperazine rings adopt a chair conformation, whereas the positions of the nitro-phenyl group on the piperazine ring differ from bis-ectional in (I) to equatorial in (II). In both structures, the supra-molecular assemblies are mono-periodic on the basis of the chain-of-rings motifs supported by aromatic π-π inter-actions. Hirshfeld surface analysis was used to explore the inter-molecular close contacts in both crystals. The most dominant contacts of the Hirshfeld surface of the cation-anion pairs of the asymmetric units are O⋯H/H⋯O, and those with a contribution of halogen atoms: F⋯H/H⋯F in (I) and Cl⋯H/H⋯Cl in (II), respectively.

On the nature of inter-anion coinage bonds.

To explore the binding energy profiles and elucidate the bonding nature in counter-intuitive anion⋯anion coinage bonds (CiBs), thirty-one complexes were constructed, and the inter-anion CiBs were studied theoretically. The metastability was evidenced by the characteristic potential wells in six cases, demonstrating that anions [Au(CN)4]-, [Ag(CN)2]- and [AuO]- are appropriate building blocks for CiBs. The kinetic stability was further supported by ab initio molecular dynamics (AIMD) simulations and the analyses based on the local vibrational mode and quantum theory of atoms in molecules (QTAIM) methods. The anion⋯anion CiBs in the dimers of [AuCl4]- and [Au(CN)4]- previously observed in condensed phases were confirmed to be thoroughly repulsive under vacuum, but turned attractive in the crystal environment which was simulated using the solvation model based on density (SMD). However, the intrinsic strength of the inter-anion bonding is barely variated by the environment, as it is the combination of the inter-anion interaction and the environment effect that stabilizes the anion pairs. The block-localized wavefunction (BLW) method and its corresponding energy decomposition (BLW-ED) approach were further employed aiming at a chemically meaningful explanation for these counterintuitive phenomena. By inspecting the profiles of energy components, we identified the vital distinction between inter-anion CiBs and conventional non-covalent interactions lying in the electrostatic interaction, which variates nonmonotonically in the inter-anion complexes. The electrostatic interaction also dominates the depth of potential wells, which is commonly used to evaluate the kinetic stability, while Pauli exchange repulsion is the most repulsive factor preventing the formation of anion adducts. The importance of the Pauli exchange repulsion was further highlighted by comparing cases with and without metastability, in which the absence of a potential well is solely caused by the enhancement of the Pauli exchange repulsion.

Thermoresponsive Ionic Liquid with Different Cation-Anion Pairs as Draw Solutes in Forward Osmosis.

We synthesized various phosphonium- and ammonium-based ionic liquids (ILs), using benzenesulfonate (BS) and 4-methylbenzenesulfonate (MBS) to establish the criteria for designing an ideal draw solute in a forward osmosis (FO) system. Additionally, the effects of monocationic, dicationic, and anionic species on FO performance were studied. Monocationic compounds ([P4444][BS], [P4444][MBS], [N4444][BS], and [N4444][MBS]) were obtained in one step via anion exchange. Dicationic compounds ([(P4444)2][BS], [(P4444)2][MBS], [(N4444)2][BS], and [(N4444)2][MBS]) were prepared in two steps via a Menshutkin SN2 reaction and anion exchange. We also investigated the suitability of ILs as draw solutes for FO systems. The aqueous [P4444][BS], [N4444][BS], [N4444][MBS], and [(N4444)2][BS] solutions did not exhibit thermoresponsive behavior. However, 20 wt% [P4444][MBS], [(P4444)2][BS], [(P4444)2][MBS], and [(N4444)2][MBS] had critical temperatures of approximately 43, 33, 22, and 60 °C, respectively, enabling their recovery using temperature. An increase in IL hydrophobicity and bulkiness reduces its miscibility with water, demonstrating that it can be used to tune its thermoresponsive properties. Moreover, the FO performance of 20 wt% aqueous [(P4444)2][MBS] solution was tested for water flux and found to be approximately 10.58 LMH with the active layer facing the draw solution mode and 9.40 LMH with the active layer facing the feed solution.

Thermally Activated Aromatic Ionic Dopants (TA‐AIDs) Enabling Stable Doping, Orthogonal Processing and Direct Patterning

AbstractDoping plays a critical role in organic electronics, and dopant design has been central in the development of functional and stable doping. In this study, there is departure from conventional molecular dopants and a new class of dopants are reported – aromatic ionic dopants (AIDs). AIDs consist of a pair of aromatic cation and anion that are responsible for molecular doping reaction and charge balancing separately. It is shown that the first AID made from cycloheptatrienyl (tropylium) cation and pentacyanocyclopentadienide anion (PCCp), abbreviated as T‐PCCp, can function as an effectivep‐type dopant to dope polydioxythiophenes. Here, tropylium cation induces the doping reaction while the PCCp anion stabilizes the generated polarons and bipolarons. With T‐PCCp, a highly doped (≈120 S/cm) and stable system is achieved up to 150 °C, an orthogonal (sequential)solution processing resulting from the immiscibility of the dopant and the polymer host, and a high‐resolution direct micropatterning with laser writing resulted from a thermally activated doping process.

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.