Cationic Substituents Research Articles

Assembled Structures and Electrical Conductivities of Salts Comprised of Cationic Sandwich Complexes and Polyoxometalates.

Polyoxometalates (POMs) are recognized for their diverse structures and catalytic properties, yet their organometallic salts have not been thoroughly investigated. In this study, we synthesized salts of a Keggin-type POM with cationic sandwich complexes featuring various substituents, [X]2[SMo12O40] [X = Ru(C5H5)(C6H5R); R = H (1a), Me (1b), Bu (1c)], [Co(C5H5)2 (2), and Co(C5Me5)2 (3)]. These salts exhibited similar structural characteristics, with each anion surrounded by 10 cations, forming two-dimensional sheet arrangements through O···O anion-anion contacts, except for the salt of 1c, which exhibited one-dimensional contact owing to the larger cation substituent. Additionally, [2](THA)[Mo6O19], [3]2[Mo6O19], and [3](THA)[SMo12O40], containing the Lindqvist-type POM [Mo6O19] and/or tetrahexylammonium (THA) cation, were obtained, with the packing structure of [3]2[Mo6O19] closely resembling that of [X]2[SMo12O40]. Solvate crystals of [1a]3[PMo12O40] were also prepared. [1a]2[SMo12O40] exhibits an electrical conductivity σ of 1.4 × 10-7 S cm-1 at 373 K, which is 2 orders of magnitude higher than those of (THA)2[SMo12O40] and [1a]PF6.

Exploring the effects of the alkaline earth metal cations on the electronic structure, photostability and radiation hardness of lead halide perovskites

The growing interest to the application of perovskite solar cells (PSC) in aerospace requires great attention to the design of new absorber materials with enhanced photostability and radiation hardness. We addressed this challenge through the B-site engineering by partial replacing of Pb2+ in the complex halides with Ca2+, Sr2+, and Ba2+. Change in the material electronic properties suggests the incorporation of the substituent cations in the perovskite lattice. However, when the loading of alkaline earth halides is high, they tend to segregate to the film surface and grain boundaries. The modification of MAPbI3 and Cs0.12FA0.88PbI3 by replacing a 1% of Pb2+ with alkaline earth metal cations resulted in improvements in the photostability and radiation hardness under exposure to gamma rays and electrons beam. Depending on the material formulation, it was possible to mitigate the photochemical and radiation-induced Pb0 formation and the univalent cation phase segregation. The best of the designed perovskite absorbers could successfully tolerate high doses of gamma rays (5.5 MGy) and electron fluences (3 × 1016 e/cm2), thus outperforming significantly the non-modified material. These findings feature the incorporation of alkaline earth metal cations as a promising approach for the development of PSC with enhanced radiation hardness for aerospace applications.

A Single Model for the Thermodynamics and Kinetics of Metal Exsolution from Perovskite Oxides.

Exsolution has emerged as an outstanding route for producing oxide-supported metal nanoparticles. For ABO3-perovskite oxides, various late transition-metal cations can be substituted into the lattice under oxidizing conditions and exsolved as metal nanoparticles after reduction. A consistent and comprehensive description of the point-defect thermodynamics and kinetics of this phenomenon is lacking, however. Herein, supported by hybrid density-functional-theory calculations, we propose a single model that explains diverse experimental observations, such as why substituent transition-metal cations (but not host cations) exsolve from perovskite oxides upon reduction; why different substituent transition-metal cations exsolve under different conditions; why the metal nanoparticles are embedded in the surface; why exsolution occurs surprisingly rapidly at relatively low temperatures; and why the reincorporation of exsolved species involves far longer times and much higher temperatures. Our model's foundation is that the substituent transition-metal cations are reduced to neutral species within the perovskite lattice as the Fermi level is shifted upward within the bandgap upon sample reduction. The calculations also indicate unconventional influences of oxygen vacancies and A-site vacancies. Our model thus provides a fundamental basis for improving existing, and creating new, exsolution-generated catalysts.

Charge-Enhanced Reactivity of Esters by a Cationic Substituent.

In this study, the high electrophilicity of carbonyl carbons attached to cationic heterocycles was observed. Triazolium-substituted esters underwent catalyst-free amidation with aliphatic amines at -50 °C and reduction with NaBH4 at -100 °C. The origin and generality of the high reactivity of these esters were systematically investigated. The findings of this work were utilized for the postmodification of N-heterocyclic carbenes, which are utilized as promising ligands in a wide range of transition-metal-catalyzed reactions.

Controlling Ionic Conductivity in Organometallic Ionic Liquids through Light-Induced Coordination Polymer Formation and Thermal Reversion.

Owing to their high ionic conductivity and negligible vapor pressure, ionic liquids (ILs) find applications in various electronic devices. However, fabricating IL-based photocontrollable devices remains a challenge. In this study, we developed organometallic ILs with reversible light- and heat-controlled ionic conductivities for potential use in tunable devices. The physical properties and stimulus responses of ILs containing a cationic sandwich Ru complex with two coordinating substituents were investigated. UV photoirradiation of these ILs triggered cation photodissociation, resulting in their transformation into viscoelastic coordination polymers wherein the coordinating substituents bridged the Ru centers. Owing to the anion coordination, salts with coordinating anions such as CF3SO2NCN-, B(CN)4-, and BF2(CN)2- exhibited faster response and higher conversion than those with noncoordinating anions including (FSO2)2N- and (CF3SO2)2N-. All photoproducts reverted to their original ILs upon heating, except for the photoproduct of the BF2(CN)2 salt, which decomposed upon heating. Light- and heat-induced reversible changes occur in most cases between the high-ionic-conductive IL state and low-ionic-conductive coordination polymer state. Unlike previously reported ILs with three or one cation substituent, the current ILs exhibited both high reactivity and large ionic conductivity changes.

Trimeric and Tetrameric Cationic Styryl Dyes as Novel Fluorescence and CD Probes for ds-DNA and ds-RNA.

The wide use of mono- or bis-styryl fluorophores in biomedical applications prompted the presented design and study of a series of trimeric and tetrameric homo-analogues, styryl moieties arranged around a central aromatic core. The interactions with the most common biorelevant targets, ds-DNA and ds-RNA, were studied by a set of spectrophotometric methods (UV-VIS, fluorescence, circular dichroism, thermal denaturation). All studied dyes showed strong light absorption in the 350-420 nm range and strongly Stokes-shifted (+100-160 nm) emission with quantum yields (Φf) up to 0.57, whereby the mentioned properties were finely tuned by the type of the terminal cationic substituent and number of styryl components (tetramers being red-shifted in respect to trimers). All studied dyes strongly interacted with ds-DNA and ds-RNA with 1-10 nM-1 affinity, with dye emission being strongly quenched. The tetrameric analogues did not show any particular selectivity between ds-DNA or ds-RNA due to large size and consequent partial, non-selective insertion into DNA/RNA grooves. However, smaller trimeric styryl series showed size-dependent selective stabilization of ds-DNA vs. ds-RNA against thermal denaturation and highly selective or even specific recognition of several particular ds-DNA or ds-RNA structures by induced circular dichroism (ICD) bands. The chiral (ICD) selectivity was controlled by the size of a terminal cationic substituent. All dyes entered efficiently live human cells with negligible cytotoxic activity. Further prospects in the transfer of ICD-based selectivity into fluorescence-chiral methods (FDCD and CPL) is proposed, along with the development of new analogues with red-shifted absorbance properties.

A step closer to sustainable CO2 conversion: Limonene carbonate production driven by ionic liquids

This work aims to advance the biocarbonate concept by developing the first process to produce limonene carbonate based on ionic liquids (ILs). Conventional petroleum-derived cyclic carbonates are recognized products partially composed of CO2 with the main drawback of the high energy consumption that imposes epoxide production. In contrast, natural epoxidable compounds, such as terpenes, stand out in the literature as a more sustainable open research line to enable CO2 conversion processes with better sustainable indicators. Limonene, an abundant natural compound, is identified as a key terpene in the aforementioned discussion. Ammonium-based ILs are experimentally selected and optimized, after covering massive anion and cation substituent tuning, achieving high selectivity and competitive yields to limonene carbonate. The reaction-extraction platform concept, which recovers the catalyst by liquid-liquid extraction, is envisioned and developed using a rational experimental-computational approach. The work concludes with a novel process to effectively produce limonene carbonate by using an IL catalyst and water as an extracting solvent. Ultimately, taking advance of the process simulation, a CO2 emissions assessment was conducted. Using renewable raw materials enhances the sustainability of CO2 conversion to cyclic carbonate, reducing global warming impact compared to fossil-based epoxides. However, limonene extraction and epoxidation have a tangible impact on the overall result of CO2 balance, turning efforts outside battery limits of the CO2 conversion process in the search of a limonene carbonate production line with negative neat CO2 emissions that may change the paradigm in the fixation of CO2 through cycloaddition reactions.

Interplay between cation composition and charge transport characteristics in GAxFAyMA1-x-yPbI3 halide perovskites

Halide perovskites (HPs) are a well-known class of mixed electronic and ionic conductors with diverse applications in optoelectronic devices. The simultaneous transport of ionic and electronic carriers has beneficial and detrimental effects depending on the intended applications. There is an extensive understanding of the charge transport characteristics in HPs since the phenomenon is of applied relevance. However, considering that several applications use compositions containing mixed cations, a deeper understanding of how the degree of substitution and the characteristics of the substituent cations affect the charge transport characteristics is needed. To this end, we experimentally studied the ionic conductivity (σion), current–voltage hysteresis (J–E hysteresis), mobility (μe) and density (ne) of electronic carriers, and bandgap energies (Eg) of up to 24 compositions of methylammonium lead iodide partially substituted with guanidinium and formamidinium. The results indicate that σion, J–E hysteresis, and μe decrease with the degree of substitution, with the J–E hysteresis being smaller the larger size of the substituent cation. At the same time, σion appears to be lower in compositions with equimolar substituents, in which the entropy of mixing is maximum. On the other hand, a slight increase in ne was observed with the substitution degree, showing highest values for FA+-rich compositions, where Eg is the lowest. The results advance the understanding of how it is possible to customize charge transport properties through the rational design of compositions in HPs.

Molecular mechanism for the absorption of ketone volatile organic compounds by ionic liquids

With the development of industry, volatile organic compounds (VOCs) have received increasing attention as a class of pollutants that need to be eliminated due to their adverse effects on the environment and human health. As a new green solvent, ionic liquids (ILs) are regarded as the excellent alternative to traditional organic absorbents. To investigate the effect of IL structure on its capture of VOCs, [BMIM][TF2N], [BIM][TF2N], and [EIM][TF2N] were used as acetone absorbents in this work, and the mechanism was revealed microscopically by quantum chemical calculations in conjunction with the COSMO-RS model. The results suggested that acetone tends to bind to protonic ILs more than the same type of nonprotonic ILs. For protonic ILs, changing the length of the cationic substituent has little effect on the results. Therefore, ILs with short substituent can increase the mass absorption of acetone without essentially changing the mole absorption, thus facilitating the industrial application.

Physical properties of ferromagnetic Mn-doped double perovskites (DPs) Cs2AgInCl/Br6 for spintronics and solar cell devices: DFT calculations.

A computational framework based on density functional theory (DFT) has been effectively employed to investigate the wide-ranging physical characteristics of ferromagnetic manganese (Mn)-substituted double perovskites (DPs) with composition Cs2AgIn1-xMnxCl/Br6 (x = 0.0, 0.25). This research covers a systematic exploration of the mentioned DPs for potential applications in the domains of spintronics and energy conversion devices. The physics concerning ferromagnetic (FM) Cs2AgIn0.75Mn0.25Cl/Br6 DPs was studied computationally using the modified Becke-Johnson (mBJ-LDA) potential and the generalized gradient approximation (PBEsol GGA) method introduced by Perdew, Burke, and Ernzerhof. The structural, electronic, magnetic, and transport behavior of materials were investigated using these computations. Structural parameters for both perovskite materials were computed subsequent to their optimization in FM phase. According to evaluations of the electronic band structure and density of states (DOS), the incorporation of Mn ions into the host lattice causes exchange splitting induced by p-d hybridization, consequently stabilizing the FM state. Probing the sharing of magnetic moment, charge, and spin between the substituent cations and the host anions led to the comprehensive elaboration of this exchange splitting of bands. Important parameters such as exchange constants (N0α, N0β), and direct spin-exchange splitting Δx(d), support the stability of the FM state. Finally, we briefly explored the spin effect on other aspects of electronic transport, the Seebeck coefficient, and the power factor, using the conventional Boltzmann transport theory.

Interstitial or interstitialcy: effect of the cation size on the migration mechanism in NaSICON materials.

Sodium superionic conductors (NaSICONs) with general formula NaM2A3O12 have attracted significant attention as solid electrolytes for all solid-state batteries owing to their remarkable room temperature ionic conductivity in the order of 10-3 S cm-1. Their flexible structural framework, which allows the incorporation of various aliovalent cations, affects the Na+ ion transport. However, establishing a straightforward correlation between Na+ mobility and NaSICON composition proves challenging due to competing influences such as framework alteration and stoichiometric changes of the cation substituents and thus the mobile Na+ ions. Therefore, we systematically investigate the NaSICON system across various Na1+xM2SixP3-xO12 compositions. We unravel and examine independently two key aspects impacting the Na+ ion transport in NaSICONs: structural factors determined by introduced M4+ framework cations and the substitution level (x). By employing DFT calculations, we explore the interstitial- and interstitialcy-like migration mechanisms, revealing that these mechanisms and the associated migration energies are primarily influenced by metastable transient states traversed during the Na+ ion migration. The stability of these transient states, in turn, depends on the spatial arrangement of the Na+ ions, the size of the M4+ cations defining the structural framework, and x. This study enhances our fundamental understanding of Na+ ion migration within NaSICONs across a wide range of compositions. The findings offer valuable insights into the microscopic aspects of NaSICON materials and provide essential guidance for prospective studies in this field.

Organic cations in halide perovskite solid solutions: exploring beyond size effects.

Halide perovskites are a class of materials of consolidated optoelectronic and electrochemical applications, reaching efficiencies compared to established materials in respective fields. In this scenario, the design and understanding of composition-structure-property relations is imperative. In solid solutions containing mixed cations, some direct relations between the sizes of the substituents and the properties of perovskites are generally observed. However, in several cases, these relations are not observed, implying that other characteristics of these cations play a major role. Despite its importance, this understanding has not been comprehensively deepened. To address this issue, we synthesized and characterized the structure, electrical behavior, and stability of methylammonium lead iodide-based perovskites with equal amounts of the substituents guanidinium, ethylammonium, and acetamidinium. These three large organic cations have essentially equal sizes but other remarkably different characteristics, such as the number of N-H bonds, intrinsic dipole moment, and order of C-N bonds. Herein, we show that these cations have dramatically different effects over important fundamental and applied properties of resulting perovskites, including the orthorhombic-to-tetragonal and tetragonal-to-cubic phase transitions, microstructural development, ionic conductivity, I-V hysteresis, electronic carrier mobility, and stability against light-induced degradation. These effects are correlated with the characteristics of the large substituent cations and help pave the way for a better rational chemical design of halide perovskites.

Comparatively sonophotochemical and photochemical studies of phthalocyanines with cationic substituents on nonperipheral positions.

The term sonophotodynamic therapy (SPDT) refers to a combination of sonodynamic therapy (SDT) and photodynamic therapy (PDT), in which the efficacy of the treatment is boosted by utilizing the proper amount of a sensitizer that is responsive to both light and ultrasound. Although it has been proven in photophysicochemical studies that SPDT enhances singlet oxygen production, related studies in the literature are very limited. Considering this situation, this study aims to investigate the efficacy of synthesized phthalocyanines in terms of PDT and SPDT. The singlet oxygen quantum values calculated as 0.13 for 5, 0.44 for 6, and 0.61 for 7 in photochemical (PDT) application increased to 0.18, 0.86, and 0.92, respectively, with sonophotochemical (SPDT) application. According to the results, singlet oxygen production was more efficient with SPDT. This work will add to the body of knowledge on employing the SPDT approach to increase singlet oxygen generation.

Theoretical Insight into the Imidazolium-Based Ionic Liquid Interface Structure and Differential Capacitance on Au(111): Effects of the Cationic Substituent Group.

Electric double layers (EDLs) play a key role in the electrochemical and energy storage of supercapacitors. It is important to understand the structure and properties of EDLs. In this work, quantum chemical calculations and molecular dynamics (MD) simulations are used to study the microstructure of EDLs of four different substituents of imidazolium-based bis(trifluoromethylsulfonyl)imide ionic liquids (ILs) on the Au(111) surface. It is shown that the particle interactions influence the different arrangements of the anion and cation. More alkyl substitutions and longer alkyl chains result in a higher ELUMO and thus a stronger interaction energy between cations and electrodes. Strong interactions produce linear patterns of anions/cations on the electrode and a maximum value of differential capacitance near PZC, whereas weak interactions generate worm-like patterns of anions/cations on Au(111) and a minimum value of differential capacitance near the PZC. We hold the opinion that the alkyl substitution has more effects on the EDLs. Our analysis provides a new perspective on EDLs structures at the atomic and molecular level. This study provides a good basis and guidance for further understanding the interface phenomena and characteristics of ionic liquids in electrochemical and energy device applications.

DFT study of the stabilization preconditions of the indoline spiropyrans with a cationic substituent

The computational modeling results are presented in the defining points of the isomerization process of the spiropyrans with cationic vinyl-3H-indolium substituent in the positions 6' and 8' of the 2H-chromene moiety taking into account DMSO solvent. The role of effective conjugation is revealed, that determines the significant difference in the behavior of the studied systems, based on the data of NBO energetic analysis and the atomic charge transfer analysis. The model shows that the interaction between an anion and a cation in these compounds has predominantly electrostatic nature without chemical bonds in the NBO terms

Cationic fluorescent carbon dots with solution ultra-stability and its rapid/on-site sensing application for HClO

Carbon dots (CDs) as a remarkable fluorescent nanomaterial have the advantages of easy preparation, good photostability and high sensitivity. However, the poor aqueous solution stability of carbon dots largely limited their practical application due to the characteristic of easily forming precipitation for long time storage. Here, a kind of cationic fluorescent carbon dots CDs-P(Ph)3 was designed by introducing a cationic compound, (4-carboxybutyl) triphenyl phosphonium bromide, to construct an electrostatic shell outside the dots. Such electrostatic shell could highly improve carbon dots stability in an aqueous solution to make CDs-P(Ph)3 stable for long-term storage with negligible aggregation. Meanwhile, the sensitivity of CDs-P(Ph)3 for hypochlorous acid (HClO) was also enhanced on the basis of the electron-withdrawing effect of cationic substituents on the surface of carbon dots. The limit of detection of CDs-P(Ph)3 for HClO was as low as ∼0.32 μM. Additionally, the fluorescence of CDs-P(Ph)3 could be rapid quenched by HClO with a quenching efficiency of more than 80% within 30 s. The excellent stability of CDs-P(Ph)3 in an aqueous solution made it suitable for on-site detecting HClO in real samples, such as tap, well and lake water. Such designed fluorescent nanomaterial would provide a practical application pathway for optical sensing detection in environmental samples.

Differing Effects of Mixed A-Site Composition on the Properties of Hybrid Lead Iodide Perovskites

Halide perovskites (HPs) appeared as a revolutionary class of relevant optoelectronic materials. Optimizing these materials involves developing mixed formulations currently used in many of the most efficient HP-based devices. Mixing A-site organic cations has been a widely used strategy to achieve the desired characteristics in these perovskites. Few of the reported works were devoted to understanding the effects of different organic cations on the properties of the resulting HPs. In the present work, we report a detailed study on the structural, thermal, and electrical properties and degradation assays in HPs with mixing A-site organic cations at the MAPbI3, FA0.10MA0.90PbI3, GA0.10MA0.90PbI3, and GA0.05FA0.05MA0.90PbI3 compositions. The results show that the charge transport properties change consistently with the A-site cation size. However, the structure and phase transitions are unusually affected by the composition, suggesting that other characteristics of substituent cations are relevant to the behavior of the resulting materials. Finally, thermal degradation tests reveal that, contrary to general expectations, not all mixed compositions are more stable than their related pure HPs. More than that, the order of degradation kinetics may also depend on the type of substituent cation. The results elucidate the particularities of each type of organic cation on the properties of mixed perovskites and advance knowledge about these relevant materials.

Modular preparation of cationic bipyridines and azaarenes via C-H activation.

Bipyridines are ubiquitous in organic and inorganic chemistry because of their redox and photochemical properties and their utility as ligands to transition metals. Cationic substituents on bipyridines and azaarenes are valuable as powerful electron-withdrawing functionalities that also enhance solubility in polar solvents, but there are no general methods for direct functionalization. A versatile method for the preparation of trimethylammonium- and triarylphosphonium-substituted bipyridines and azaheterocycles is disclosed. This methodology showcases a C-H activation of pyridine N-oxides that enables a highly modular and scalable synthesis of a diverse array of cationically charged azaarenes. The addition of trimethylammonium functionalities on bipyridine derivatives resulted in more anodic reduction potentials (up to 700 mV) and increased electrochemical reversibility compared to the neutral unfunctionalized bipyridine. Additonally, metallation of 4-triphenylphosphinated biquinoline to make the corresponding Re(CO)3Cl complex resulted in reduction potentials 400 mV more anodic than the neutral derivative.

Electrocatalytic oxygen reduction with cobalt corroles bearing cationic substituents.

Recent decades have seen increasing interest in developing highly active and selective electrocatalysts for the oxygen reduction reaction (ORR). The active site environment of cytochrome c oxidases (CcOs), including electrostatic and hydrogen-bonding interactions, plays an important role in promoting the selective conversion of dioxygen to water. Herein, we report the synthesis of three CoIII corroles, namely 1 (with a 10-phenyl ortho-trimethylammonium cationic group), 2 (with a 10-phenyl ortho-dimethylamine group) and 3 (with a 10-phenyl para-trimethylammonium cationic group) as well as their electrocatalytic ORR activities in both acidic and neutral solutions. We discovered that 1 is much more active and selective than 2 and 3 for the electrocatalytic four-electron ORR. Importantly, 1 showed ORR activities with half-wave potentials at E1/2 = 0.75 V versus RHE in 0.5 M H2SO4 solutions and at E1/2 = 0.70 V versus RHE in neutral 0.1 M phosphate buffer solutions. This work is significant for outlining a strategy to increase both the activity and selectivity of metal corroles for the electrocatalytic ORR by introducing cationic units.

Local Structure in α-BIMEVOXes (ME = Ge, Sn).

The BIMEVOXes are among the best oxide ion conductors at low and intermediate temperatures. Their high conductivity is associated with local defect structure. In this work, the local structures of two BIMEVOX compositions, Bi2V0.9Ge0.1O5.45 and Bi2V0.95Sn0.05O5.475, are examined using total neutron and X-ray scattering methods, with both compositions exhibiting the ordered α-phase at 25 °C and the disordered γ-phase at 700 °C. While the diffraction data for the α-phase do not allow for the polar (C2) and nonpolar (C2/m) structures to be readily distinguished, measurements of dielectric permittivity suggest the α-phase is weakly ferroelectric in character, consistent with calculations of spontaneous polarization based on a combination of density functional calculations and machine learning methodology. Reverse Monte Carlo (RMC) analysis of total scattering data reveals Ge preferentially adopts tetrahedral geometry at both temperatures, while Sn is found to predominantly adopt octahedral coordination in the α-phase and tetrahedral coordination in the γ-phase. In all cases, V polyhedra are found to consist of tetrahedral, pentacoordinate, and octahedral geometries, as also predicted by the crystallographic analysis and confirmed by 51V solid state NMR spectroscopy. Although similar long-range structures are observed at room temperature, the oxide ion vacancy distributions were found to be quite different between the two studied compositions, with a nonrandom deficiency in vacancy pairs in the second-nearest shell along the ⟨100⟩ tetragonal direction for BIGEVOX10, compared with a long-distance (>8.0 Å) ordering of equatorial vacancies for BISNVOX05. This is attributed to the differences in the preferred coordination geometries of the substituent cations in the two systems. Impedance spectroscopy measurements reveal both compositions show high conductivity in the order of 10-1 S cm-1 at 600 °C.