TBA Cations Research Articles

Mechanochemical Polyoxometalate Super-Reduction with Lithium Metal.

In this first systematic investigation of mechanochemical polyoxometalate (POM) reduction, (TBA)3[PMo12O40] was reacted with n equiv of lithium metal (n = 1-24) to generate PMo12/n products which were shown to be mixtures of electron-rich PMo12Lix species. FTIR analysis revealed the lengthening/weakening of terminal Mo═O bonds with increasing levels of reduction, while EXAFS spectra indicated the onset of Mo-Mo bond formation at n ∼ 8 and a significant structural change at n > 12. Successive MoVI reductions were monitored by XANES and XPS, and at n = 24, results were consistent with the formation of at least one MoIV-MoIV bonded {MoIV3} triad together with MoV. Upon dissolution, the PMo12Lix species present in the solid PMo12/n products undergo electron exchange and single-peak 31P NMR spectra were observed for n = 1-12. For n ≥ 16, changes in solid state and solution 31P NMR spectra coincided with the emergence of features in the UV-vis spectra associated with MoV-MoV and {MoIV3} bonding in an ε-Keggin structure. Bonding between {Li(NCMe)}+ and 2-electron-reduced PMo12 in (TBA)4[PMo12O40{Li(NCMe)}] suggests that super-reduction gives rise to more extensive Li-O bonding that ultimately causes lithium-oxide-promoted TBA cation decomposition and POM degradation, which might explain the appearance of XPS peaks for Mo2C at n ≥ 16. This work has revealed some of the complex, unexplored chemistry of super-reduced POMs and establishes a new, solvent-free approach in the search for a better fundamental understanding of the electronic properties and reactivity of electron-rich nanoscale metal oxides.

Exfoliation of Nanosized α-Zirconium Phosphate in Methanol

The exfoliation of microcrystalline α-zirconium phosphate (α-ZrP) in an organic solvent is very difficult to achieve. Surprisingly, the addition of tetra(n-butyl)ammonium hydroxide (TBAOH) into a methanol dispersion of a nanosized α-ZrP brings about the complete exfoliation of nanosheets. To understand the mechanism, we examined the stepwise intercalation/exfoliation of the nanosized α-ZrP using TBAOH in four different solvents (water, methanol, ethanol, and butanol). Propionate groups on the edge of the nanosized α-ZrP prevent TBA cations from entering the galleries. Due to the formation of unstable solvent-intercalated α-ZrP with an increased interlayer distance in methanol and ethanol, TBA cations can overcome the steric hindrance and move into nanosheet layers to exchange with solvent molecules. However, the movability of the cations into the center of the galleries is preferred at a certain interlayer distance range, which leads to exfoliation of α-ZrP in methanol but intercalation only in ethanol. In water, in the beginning, neither intercalation nor exfoliation by TBA cations occurs. An additional amount of TBAOH causes the deformation of propionate groups and removes the barriers on the edges, followed by late intercalation and then exfoliation. On the other hand, butanol, as the solvent, is bulky and effectively limits the intercalation behavior of TBA cations. The weaker polarity of ethanol and butanol, compared with water and methanol, lowers the ion interactions in the solvent, which is another reason why they do not lead to exfoliation.

Organic Tetrabutylammonium Cation Intercalation to Heal Inorganic CsPbI3 Perovskite.

The in situ formation of reduced dimensional perovskite layer via post-synthesis ion exchange has been an effective way of passivating organic-inorganic hybrid perovskites. In contrast, cesium ions in Cs-based inorganic perovskite with strong ionic binding energy cannot exchange with those well-known organic cations to form reduced dimensional perovskite. Herein, we demonstrate that tetrabutylammonium (TBA+ ) cation can intercalate into CsPbI3 to effectively substitute the Cs cation and to form one-dimensional (1D) TBAPbI3 layer in the post-synthesis TBAI treatment. Such TBA cation intercalation leads to in situ formation of TBAPbI3 protective layer to heal defects at the surface of inorganic CsPbI3 perovskite. The TBAPbI3 -CsPbI3 perovskite exhibited enhanced stability and lower defect density, and the corresponding perovskite solar cell devices achieved an improved efficiency up to 18.32 % compared to 15.85 % of the control one.

Organic Tetrabutylammonium Cation Intercalation to Heal Inorganic CsPbI3 Perovskite

AbstractThe in situ formation of reduced dimensional perovskite layer via post‐synthesis ion exchange has been an effective way of passivating organic‐inorganic hybrid perovskites. In contrast, cesium ions in Cs‐based inorganic perovskite with strong ionic binding energy cannot exchange with those well‐known organic cations to form reduced dimensional perovskite. Herein, we demonstrate that tetrabutylammonium (TBA+) cation can intercalate into CsPbI3 to effectively substitute the Cs cation and to form one‐dimensional (1D) TBAPbI3 layer in the post‐synthesis TBAI treatment. Such TBA cation intercalation leads to in situ formation of TBAPbI3 protective layer to heal defects at the surface of inorganic CsPbI3 perovskite. The TBAPbI3‐CsPbI3 perovskite exhibited enhanced stability and lower defect density, and the corresponding perovskite solar cell devices achieved an improved efficiency up to 18.32 % compared to 15.85 % of the control one.

Ionic Clathrate Hydrates of Tetra-n-Butylammonium Nitrate (TBANO3) and Mixed TBA(NO3,OH): Novel Superstructures of Tetragonal Structure I

The structures of an ionic clathrate hydrate of tetra-n-butylammonium nitrate TBANO3·26.7H2O and mixed TBA(NO3)1−x(OH)x·(31.5 − x)H2O hydrate obtained from a mixture of tetra-n-butylammonium nitrate and tetra-n-butylammonium hydroxide are determined by single crystal X-ray diffraction. These structures are new types of superstructures based on classical tetragonal structure I with four- and twofold unit cells volumes for TBANO3·26.7H2O and TBA(NO3)1−x(OH)x·(31.5 − x)H2O respectively. The superstructures form as a result of ordering in the arrangement of multicompartment cavities of the water-anionic framework. A TBA cation is displaced from the center of combined cavities due to the anisotropic environment of the anions, which leads to an additional symmetry reduction. The modes of the nitrate anion incorporation into the water framework of ionic clathrate hydrates are determined for the first time.

Phase transitions and transport properties in tetra-n-butylammonium iodide

A remarkable feature of organic salts is easy reorientation of organic groups, especially in high-temperature phases. It would be expected that the reorientational motion of organic groups promotes also ion transport processes within the crystal structure. In this work thermal and transport properties of solid organic salt (n-C4H9)4NI were investigated by methods of DSC, dilatometry, conductivity measurements and NMR spectroscopy. It was proposed that three low-temperature phases, II, III and IV, along to the high-temperature phase I appear in this salt after heat treatment. The conductivity and temperature stability range of the low-temperature phases depend on conditions of the heat treatment of the salt. Temperature intervals of stability of phases II and III considerably increases after prolonged heating in the melt. In parallel, the conductivity of all low-temperature phases increases in contrast to the conductivity of the phase I. These facts may be explained by the formation of extrinsic iodine vacancies as a result of the dissolution of tributylanine formed at partial thermal decomposition of the salt. According to 1H NMR data, in high-temperature phase TBA cations are mobile. No information on anionic diffusion in this phase was obtained due to a low intensity of 127I NMR spectra. The most mobile defects in low-temperature phases of (n-C4H9)4NI seem to be iodine vacancies.

Exploiting cooperative binding of ion-pair to boost anion recognition in water/acetonitrile mixtures

An L-arginine based compound was designed and prepared as a heteroditopic ion-pair receptor. The cation binding is provided by a sodium selective N-acyl-aza-18-crown-6 subunit whereas for anion complexation, urea and guanidinium groups were introduced. As shown by 1H NMR titrations this receptor is capable of binding sodium halide ion-pairs in solutions containing up to 20% of water. The halide binding is stronger in the presence of co-coordinated sodium cation than in the presence of non-coordinated TBA cation.

Dielectric properties of single crystal Sr 2 Nb 3 O 10 dielectric nanosheet thin films by electrophoretic deposition (EPD) and post deposition treatments

Abstract Sr2Nb3O10 (SNO) nanosheets were obtained by exfoliating from a perovskite layered structure of HSr2Nb3O10 (HSNO). The nanosheets were deposited on substrates simultaneously with unintended tetrabutylammonium cations (TBA+) by electrophoretic deposition (EPD) process. To eliminate TBA+ from the SNO dielectric nanosheet thin films, the films were exposed to ultraviolet (UV). Since UV exposure can't decompose TBA+ completely, thermal annealing was additionally conducted by employing different furnaces at various atmospheres. XRD shows the reduction in lattice constant after UV and thermal treatments, indicating that TBA cations were decomposed in the interlayer of nanosheets. FT-IR spectra analysis depicted that the organic materials were eliminated through the post deposition treatments. In addition, XPS data indicated that films treated by a combination of UV and thermal had a lower relative atomic ratio of carbon and nitrogen than as-deposited and only-UV treated films. The optimum process conditions for improving dielectric properties were UV exposure for 15 h and subsequent thermal annealing in a box furnace in the air at 600 °C for 1 h. When compared to the as-deposited film, the dielectric constants of films further annealed by the box furnace in the air were increased from 8 to 27 at 1 MHz whereas dielectric loss (tan δ) decreased from 5% to 2%. Additional thermal treatment strongly affects nanosheets to decompose TBA+.

CO2 capture: Tuning cation-anion interaction in urethane based poly(ionic liquids)

Abstract The development of new urethane based poly(ionic liquids) (PILs) is a promising solution to address CO 2 capture. The obtainment of low cost polyurethane based PILs using different ionic liquids cations fosters the emergence of new materials for CO 2 capture. The synthesized PILs were characterized by GPC, FTIR, NMR, DSC, TGA, DMTA and AFM. CO 2 sorption capacity was gravimetrically assessed in a magnetic suspension balance. In addition, ab initio simulations were performed. Experimental and simulation results allow understanding the varying performance of the polymeric anion with the bmim, TBA, and TBP cations in CO 2 sorption. A successful compound for gas capture must exhibit the weakest possible cation-anion coordination and smaller molecular masses. Better CO 2 sorption capacity was achieved for the cation TBA as compared to TBP and bmim (the amounts of CO 2 sorption at 50 bar and 303.15 K were 162 mgCO 2 /g for the PU-bmim, 168 mgCO 2 /g for PU-TBP and 226 mgCO 2 /g PU-TBA). At lower pressures, these compounds present a high CO 2 sorption capacity (at 0.82 bar of pressure and 303.15 K PU-bmim presented a CO 2 sorption of 9.4 mgCO 2 /g; PU-TBP 15.7 mgCO 2 /g and PU-TBA 16.1 mgCO 2 /g). The compounds PU-TBP and PU-TBA presented higher sorption values as compared to literature.

Boosting the salt recognition abilities of L-ornithine based multitopic molecular receptors by harnessing a double cooperative effect.

A family of L-ornithine based salt receptors 1a-f was synthesized, bearing a cation binding site and multiple anion binding sites (nitrophenylurea and amide groups) that may simultaneously associate with a single anion. The variation in H-bond donor abilities of one of these anion binding sites has relatively little influence on NO2(-) anion binding when the anion is accompanied by a noncoordinating TBA cation. However, in the presence of a sodium cation, which strongly coordinates with the cation binding domain of 1a-f, the increased H-bond donor abilities of the anion binding group result in a significant enhancement of NO2(-) anion binding. A direct correlation between the anion binding site H-bond donor tendencies and the binding cooperation of sodium cations and nitrite anions was also observed. Cation complexation fixes the nitrophenylurea moiety orientation and exposes that domain to bind anions. This cation and anion cooperation induces a second cooperative effect, namely the simultaneous association of a single anion with both urea and amide binding groups. Receptor 1d was found to be highly selective for NaNO2 over sodium bromide and nitrate. A transport experiment using a bulky liquid membrane showed that this receptor can effectively transport NaNO2 from the aqueous phase through the organic phase.

Physicochemical and Structural Studies of Clathrate Hydrates of Tetrabutylammonium Polyacrylates

In this work, physicochemical and structural studies have been carried out for semiclathrate hydrates of linear (un-cross-linked) and cross-linked tetrabutylammonium polyacrylates with different degrees of cross-linking of the polymeric guest molecules (n = 0.5, 1, 2, 3%) and different degrees of substitution of proton ions of carboxylic groups in poly(acrylic acid) for TBA cations (x = 1, 0.8, 0.6). The changes in the hydrates' stability and composition depending on the outlined parameters were examined in the course of phase diagram studies of the binary systems water-tetrabutylammonium polyacrylates using differential thermal analysis method and calorimetric measurements of fusion enthalpies of the hydrates. Phase diagram studies of the binary system water-linear tetrabutylammonium polyacrylate revealed the formation of four hydrates. Based on the data of chemical analysis of hydrate crystals the compositions of all hydrates have been determined. Single-crystal X-ray diffraction studies revealed a tetragonal structure, space group 4/m, and unit cell parameters are close for different hydrates and lie in the ranges a = 23.4289-23.4713 Å and c = 12.3280-12.3651 Å (150 K). The structure can be related to tetragonal structure I typical for the clathrate hydrates of tetraalkylammonium salts with monomeric anions. Powder X-ray diffraction analyses confirmed the identity of the above crystal structure to that of the hydrates with cross-linked tetrabutylammonium polyacrylates. The behavior of TBA polyacrylate hydrates under the pressure of methane was studied and quantitative assessment of the gas content in the hydrates was made using volumetric analysis method.

A Series of Amino Acid Functionalized Tripodal Hexaamide Anion Receptors: Ion-Pair-Assisted Capped-Cleft Formation by a Pentafluorophenyl-Functionalized Amide

A new series of tris(2-aminoethyl)amine (tren)-based L-alanine amino acid backboned tripodal hexaamide receptors (L1-L5) with various attached moieties based on electron-withdrawing fluoro groups and lipophilicity have been synthesized and characterized. Detailed binding studies of L1-L5 with different anions, such as halides (F(-), Cl(-), Br(-), and I(-)) and oxyanions (AcO(-), BzO(-) (Bz=benzoyl), NO(3)(-), H(2)PO(4)(-), and HSO(4)(-)), have been carried out by isothermal titration calorimetric (ITC) experiments in acetonitrile/dimethylsulfoxide (99.5:0.5 v/v) at 298 K. ITC titration experiments have clearly shown that receptors L1-L4 invariably form 1:1 complexes with Cl(-), AcO(-), BzO(-), and HSO(4)(-), whereas L5 forms a 1:1 complex only with AcO(-). In the case of Br(-), I(-), and NO(3)(-), no appreciable heat change is observed owing to weak interactions between these anions and receptors; this is further confirmed by (1)H NMR spectroscopy. The ITC binding studies of F(-) and H(2) PO(4)(-) do not fit well for a 1:1 binding model. Furthermore, ITC binding studies also revealed slightly higher selectivity of this series of receptors towards AcO(-) over Cl(-), BzO(-), and HSO(4)(-). Solid-state structural evidence for the recognition of Cl(-) by this new category of receptor was confirmed by single-crystal X-ray structural analysis of the complex of tetrabutylammonium chloride (TBACl) and L1. Single-crystal X-ray diffraction clearly showed that the pentafluorophenyl-functionalized amide receptor (L1) encapsulated Cl(-) in its cavity by hydrogen bonds from amides, and the cavity of L1 was capped with a TBA cation through hydrogen bonding and ion-pair interactions to form a capped-cleft orientation. To understand the role of the cationic counterpart in solution-state Cl(-) binding processes with this series of receptors (L1-L4), a detailed Cl(-) binding study was carried out with three different tetraalkylammonium (Me(4) N(+), Et(4) N(+), and Bu(4) N(+)) salts of Cl(-). The binding affinities of these receptors with different tetralkylammonium salts of Cl(-) gave binding constants with the TBA cation in the following order: butyl>ethyl>methyl. This study further supports the role of the TBA countercation in ion-pair recognition by this series of receptors.

Methane Capacity of Double Tetrabutylammonium Bromide + Methane Ionic Clathrate Hydrates

P–T–X phase diagrams of the ternary tetrabutylammonium bromide (TBAB)–methane–water systems have been studied by differential thermal analysis under pressure up to 40 MPa and 1.2, 2.6, and 4.1 mol % TBAB. It was shown by X-ray powder diffraction that a double hydrate of TBAB + methane of hexagonal structure I (HS-I) was formed in the TBAB–methane–water system under the studied conditions. The methane capacity of the double hydrates has been measured by volumetric analysis. It was concluded that substitutional solid solution with any significant displacement of the TBA cation by methane molecules was not formed.

Potential-induced phase transition of low-index Au single crystal surfaces in propylene carbonate solution

In situ scanning tunneling microscopy (STM) was employed to examine the surface structures of Au(111), Au(100), and Au(110) single crystals in propylene carbonate (PC) containing tetrabutylammonium perchlorate (TBAP). All three electrodes exhibited potential-induced phase transition between the reconstructed and unreconstructed (1 × 1) structures at negative and positive potentials, respectively. The potential-induced phase transition of the Au electrode surfaces is attributed to the interaction of the TBA cation and the perchlorate anion at the electrode surface, which is similar to that which takes place in aqueous solutions. In addition to static atomic structures, dynamic processes of both the reconstruction and the lifting of the reconstruction were investigated by means of in situ STM. The lifting of reconstructed Au(111)-(√3 × 22) on Au(111) to the (1 × 1) structure is completed within 1 min at a positive potential. The diffusion of Au atoms on the Au(100) plane in the PC solution proceeds more rapidly than that in the aqueous solution, suggesting that the PC solvent plays an important role in accelerating the diffusion of Au atoms.

Plastic domain and ionic conductivity of (C 4H 9) 4NI

Unusual ionic transport in tetrabutylammonium iodide (C 4H 9) 4NI (TBAI) was observed by high resolution proton NMR spectroscopy accompanied by diffusion experiments. Some parts of the TBA cations are diffusing not only in the plastic phase II, but in the low temperature ordered phase I as well. The diffusing TBA ions are considered to be inside the remaining plastic domains dispersed in the ordered crystal matrix. The volume fraction of the plastic domain is evaluated from the observed narrow component of the proton NMR spectra. The observed unusual temperature dependence of the diffusion coefficient can be explained by assuming a manifold decrease of the dimension of the plastic domain in phase I. The differences in degree of crystallinity at the interface of plastic domains with respect to its surroundings led to the surface enhancement of diffusivity in phase I. Finally, the observed ionic conductivity is compared with the estimation from the diffusion coefficient and mobile cation densities. The results suggest that only a fraction of the cations take part in the observed ionic conductivity.

Room‐Temperature Nucleophilic Aromatic Fluorination: Experimental and Theoretical Studies

Room‐Temperature Nucleophilic Aromatic Fluorination: Experimental and Theoretical Studies

Counteranion Dependent Protonation and Aggregation of Tetrakis(4-sulfonatophenyl)porphyrin in Organic Solvents

The tetrabutylammonium salt of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) is soluble in dichloromethane, and the general properties of this compound have been investigated as function of various added acids HX (X = Cl, Br, I, CF(3)COO, CF(3)SO(3), TFPB) through UV-vis absorption spectroscopy, steady state fluorescence emission, and resonance light-scattering (RLS) techniques. Upon addition of HX, the initial monomeric free base TPPS is readily converted in an aggregated species, whose spectroscopic features are independent of the nature of the counteranion X. All the spectroscopic evidence suggest a J-type arrangement of chromophores in this aggregate, involving strong hydrogen bonds, electrostatic, and dispersive interactions. In the specific case of chloride and bromide, in the presence of a TBAX excess, the addition of the corresponding acid leads to a monomeric ion-pair between the TBA cations and the diacid TPPS, whose central core is strongly interacting with the halide. On further increasing the acid concentration in these latter solutions, fully protonated species are formed that eventually start to aggregate.

Phase transition and ionic transport mechanism of (C 4H 9) 4NI

Phase transition and ionic transport in tetrabutylammoniumiodide (C 4H 9) 4NI (TBAI) was investigated using X-ray diffraction, DSC, ionic conductivity and high resolution proton NMR spectroscopy. The TBAI exhibited a solid state phase transition at 391 K of Δ S = 95.2 J/mol K from an ordered phase I to a rotationally disordered plastic phase II. Ionic conductivity in phase I increased gradually near the phase transition point. On the other hand, proton NMR diffusion coefficients showed decrease with raising temperature. The observed fast diffusion of the TBA cation has significant contribution to the observed ionic conductivity of this material.

Specific swelling behaviors of poly(4-vinyl phenol) gels in tetraalkylammonium chloride solutions.

Swelling behaviors of poly(4-vinyl phenol) (P4VPh) gel in aqueous tetraalkylammonium chloride (TAACl) solutions were investigated to find a very specific swelling behavior. Especially for the tetrabutylammonium chloride (TBACl) system, P4VPh gel remarkably deswelled with increasing salt concentration (</=2.0 M) and then sharply reswelled in a higher concentration region (>/= ca. 2.1 M). A similar swelling profile was also observed in the swelling time-course; upon immersion of a water-swollen P4VPh gel into 2.5 M TBACl solution, the gel first deswelled in an early stage (approximately 0.1 h) and then remarkably reswelled with time. Relative amounts (mol/mol) of TBA cation and water per monomer residue were estimated as ca. 1 and 0 for the deswollen state and 5 and 50 for the reswollen state, respectively. This result, together with those of attenuated total reflection Fourier transform infrared measurements performed for the gels swollen in various kinds of TAACl and inorganic salt solutions, suggested that in the highly deswollen and almost dehydrated state, phenol rings aggregated with intervening TBA cations, while the aggregation reswelled upon further binding with TBA cations.

Low-Temperature Deposition of TiO2 Thin Films with Photocatalytic Activity from Colloidal Anatase Aqueous Solutions

Crystalline TiO2 films have been deposited on several substrates (glass, F-doped SnO2-covered glass, and silicon wafers) by a drain-coating method from a colloidal anatase aqueous solution. The process is performed at low-temperature, 333 K, in open atmosphere. The colloidal TiO2 consists on anatase nanoparticles of about 9 × 5 nm size, stabilized by tetrabutylammonium cations (TBA+). This colloid has also been obtained under mild conditions (i.e., low temperature and ambient pressure) by hydrolysis of tetraisopropyl orthotitanate (TIP) in the presence of (TBA)OH and subsequent treatment by microwave radiation to enhance crystallization. Different film thicknesses have been obtained by consecutive deposition processes. Titania films thus obtained were transparent and showed good adherence. FT-IR analysis of the films reveal that TBA cations were not trapped in the film during the deposition process. No further thermal posttreatment was required to eliminate organics from the films or to induce titania crystallization. The photocatalytic activity of as-deposited titania has been assessed by the photodegradation of salicylic acid in aqueous solution under aerated conditions.