Series Of Salts Research Articles

Five new isomorphic coordination polymers with large conjugated ligands: Synthesis, crystal structures and performances

Five new coordination compounds with isomorphic frameworks, {[M(cpp)2(H2O)2]·3H2O}n [M ​= ​Co (1), Cd (2), Mn (3), Ni (4), Zn (5)], were successfully synthesized through the reactions of 1-(4-carboxyphenyl)-3-(pyrazin-2-yl)pyrazole (Hcpp) and a series of transition metal salts under the solvo-thermal conditions. Compounds 1–5 were characterized by single crystal X-ray diffraction, powder X-ray diffraction, elemental analysis, infrared spectra and thermogravimetric analysis. Isomorphic compounds 1–5 display an abnormal two-dimensional helical layer containing a M4(cpp)4 cavity with the dimension of 26.21 ​× ​8.39 ​Å2. Variable-temperature magnetic susceptibility measurements indicate weak antiferromagnetic interactions with Curie constant (2.08 ​cm3 ​K ​mol−1) and Weiss constant (−6.90 ​K) in compound 1. Compounds 2 and 5 show apparently blue light emission, wherein the sensing responses to small molecules, inorganic anions and metal cations indicate compound 5 can be used as a multifunctional fluorescence probe to detect aniline, Fe3+, CrO42− and Cr2O72− through fluorescence quenching and the corresponding quenching mechanisms are proposed.

Different types of interactions between fullerene C60 and C70 anions and metal tetraphenylporphyrins in the (PMDAE+)(MIITPP)(Fullerene−)⋅Solvent complexes (M = Co, Mn, Zn) containing coordinating N, N, N, N‘, N‘-pentamethyldiaminoethane cations

Series of anionic salts of fullerenes C60 and C70 with different metal tetraphenylporphyrins, MIITPP, where M = Co, Mn and Zn, and N, N, N, N‘, N‘-pentamethyldiaminoethane cations (PMDAE+) has been obtained in a crystalline form. Composition of the complexes is (PMDAE+)⋅(MIITPP)(C60−)⋅XC6H4Cl2 (M = Co, X = 1.25 (1), M = Mn, X = 0.75 (2) and M = Zn, X = 0.75 (3)) and {(PMDAE+)⋅ZnIITPP}2⋅(C70−)2⋅4C6H4Cl2 (4). Both fullerene anion and nitrogen-containing PMDAE+ cation can coordinate to metal porphyrin competing with each other. Weak Co-C(C60−) coordination bond of 2.426(7) Å length (120 K) is formed in 1 whereas PMDAE+ cation only weakly coordinates to CoIITPP. Dissociation of Co-C(C60−) bond observed at 90–310 K is accompanied by a transition of 1 from singlet to triplet state with an energy gap of 574 ± 3 K. According to the calculations negative charge on C60− is only −0.548 due to electron transfer to the macrocyclic ligand through the cobalt atom. Charge transfer bands are observed in {CoIITPP(C60)}− at 700 and 1240 nm. On the contrary, PMDAE+ cations coordinate to MnIITPP and ZnIITPP in 2 and 3, respectively, with short M−N(PMDAE+) bonds of 2.27–2.33 Å length. In these cases fullerenes are preserved in the non-coordinated radical anion state. Fullerenes are arranged in closely packed π-stacking {C60•−}2 dimers with short interfullerene center-to-center distances of 9.92–9.95 Å. Nevertheless, the C60•− radical anions do not form intercage CC bonds down to 1.9 K. Strong antiferromagnetic coupling of spins is observed in the {C60•−}2 dimers of 3 with exchange interaction of J/kB = -21 K. Both {(PMDAE+)⋅MnIITPP} and C60•− species are paramagnetic in 2 having S = 5/2 and S = 1/2 spin states, respectively. These spins are coupled antiferromagnetically with Weiss temperature of −16 K. It is obvious that magnetic coupling occurs not only in the {C60•−}2 dimers but MnIITPP is also involved in this coupling. The C70•− radical anions are dimerized in 4 forming diamagnetic singly-bonded (C70−)2 dimers which manifest intense NIR absorption. As a result, complex 4 is EPR silent.

Bifunctional organoboron-phosphonium catalysts for coupling reactions of CO2 and epoxides.

Recent years have witnessed intensive research activity in exploring novel metal-free organocatalysts for catalyzing the coupling reactions of CO2 and epoxides to afford cyclic or polymeric carbonates. In this direction, herein we report a series of boron-phosphonium organocatalysts for catalyzing the coupling reactions of CO2 and epoxides. These organophosphonium catalysts were synthesized in high yields by following a two step protocol involving Menschutkin and hydroboration reactions in succession. The purity of these organocatalysts was confirmed by spectroscopic techniques like 1H, 13C and 31P NMR, and molecular structures were confirmed by single crystal X-ray diffraction studies. We have also demonstrated that these bifunctional organoboron-phosphonium catalysts are comparatively much less hygroscopic compared to the analogus ammonium catalysts. These phosphonium organocatalysts were shown to catalyze the copolymerization of CO2 and cyclohexene oxide or vinyl cyclohexene oxide to provide polycarbonates with >99% polymer selectivity and carbonate linkages. The coupling reactions of aliphatic epoxides such as PO, having lower energy barrier to cycloaddition formation compared to alicyclic epoxides, preferentially provided cyclic carbonates in good yields. It was demonstrated that these organoboron-phosphonium catalysts are sensitive to chain transfer agents like water, and hence are deactivated in its presence. This is opposite to what is observed for metal based catalysts for these transformations, where water serves as a precursor to the chain-transfer agent diols.

Acridinium salts as photoredox organocatalysts for photomediated cationic RAFT and DT polymerizations of vinyl ethers

A series of acridinium salts with high excited-state oxidative power are employed as photoredox organocatalysts for photomediated cationic RAFT and DT polymerizations under visible light.

The effect of substituents and their positions on a series of disubstituted naphthalene bromide salts towards intermolecular interactions and crystal packing

Naphthalene derived dications bearing different N-heterocyclic substituents appended at different positions demonstrated conformational flexibility and interesting self-assembled packing motifs when crystallised in the solid state as bromide salts.

Pressure-induced phase transition of a series of energetic pentazolate anion salts: a DFT study

The distortion angles of two energetic pentazolate salts (N5−)2DABTT2+ and N5−GU+.

The role of attractive and repulsive interactions in the stabilization of ammonium salts structures

A series of ammonium salts was used to propose a step-by-step approach to obtain the stabilization energy and contact area data of supramolecular clusters in charged molecules. A new parameter was presented to assess the cluster energy efficiency.

Nitrogen-rich ion salts of 1-hydroxytetrazole-5-hydrazide: a new series of energetic compounds that combine good stability and high energy performance.

High-efficiency explosives that combine high stability and excellent energy performance are one of the key directions of energetic materials research. In this study, a novel monocyclic hydroxytetrazole derivative (3) with high stability was prepared, and a series of insensitive energetic ionic salts were derived from it. Benefiting from their outstanding performance in terms of density, 3D hydrogen bonding and π-electron interactions, these salts are excellent in both detonation performance (D = 8709 to 9314 m s-1 and P = 29.9 to 35.6 GPa) and thermal stability (Td = 193.0-232.2 °C). The hydrazine salt (2) exhibits high detonation properties (D = 9314 m s-1 and P = 35.6 GPa), due to its high density (ρ = 1.71 g cm-3) and high heat of formation (ΔfH = 563.2 kJ mol-1 = 3.19 kJ g-1). In addition, the high thermal stability (Td = 232.0 °C) and low mechanical sensitivity (IS = 30 J and FS = 360 N) of 2 are also unmatched by HMX and TKX-50. These improved properties demonstrate the great promise of 2 as an insensitive high-energy explosive.

Synthesis of cationic π-extended imidazolium salts by sequential Cu-catalyzed arylation/annulation and photocyclization.

A series of cationic π-extended imidazolium salts were synthesized by a sequential Cu-catalyzed arylation/annulation and photocyclization strategy in a simple but efficient way. Among them, a nine-fused-ring compound with a doubly aza[5]helical geometry is by far the largest cationic polycyclic heteroaromatic with a central imidazolium core.

Thermal, structural and dynamic properties of ionic liquids and organic ionic plastic crystals with a small ether-functionalised cation

A series of new salts with a small ether-functionalised trimethylammonium cation are synthesised and characterised to probe their unique structure–property relationships.

CO2 fixation into cyclic carbonates catalyzed by single-site aprotic organocatalysts

The catalytic activity of a series of onium salts for the synthesis of cyclic carbonates have been investigated experimentally and theoretically.

Hydrogen evolution-enabled rhodaelectro-catalyzed [4+2] annulations of purines and 7-deazapurines with alkynes.

A rhodium-catalyzed electrochemical regioselective annulation of 6-phenylpurines and 6-phenyl-7-deazapurines with alkynes has been developed. Electricity is used to recycle the active rhodium-based catalyst, promote the evolution of H2 and help in reducing the reaction temperature. This mild and green method enables a broad substrate scope and wide functional group tolerance, providing a new series of polycyclic purinium and 7-deazapurinium salts in high yields. Mechanistic studies show that the five-member rhodium(III) species and purinoisoquinolinium-coordinated rhodium(I) complex are the two key intermediates in this transformation.

Promotion of the photoacid generation performance of sulfonium salts by inhibiting the isomerization of conjugated systems using a cyclization strategy

AbstractThis work describes an original structure−reactivity relationship within a series of sulfonium salts synthesized using a cyclization strategy. The new sulfonium salt comprises a stilbene subunit decorated with a combination of cyclized structure, that is, carbocyclic ring, furan ring, and thiophene ring, to inhibit the isomerization of double bond systems. The photoacid generation efficiency of such cyclized stilbene derivative sulfonium salts is mainly modulated by the five‐membered ring structures and the substituent as confirmed by photodegradation, in situ nuclear magnetic resonance, and cyclic voltammetry. Such cyclization drastically regulates the population of highly reactive excited singlet species and thus enhances the photoacid generation performance of the sulfonium salts by more than one order of magnitude within the series, especially when introducing oxygen to form the benzofuran ring structure. Given this amplified photoreactivity, the application potential of the photoinitiated cationic polymerization of the sulfonium salts was evaluated at different irradiation wavelengths.

Insight into the nanostructure of “water in salt” solutions: A SAXS/WAXS study on imide-based lithium salts aqueous solutions

“Water-in-salt” electrolyte (WISE) series have been studied for lithium-ion batteries and supercapacitor applications, but so far, most of the focus has been on the LiTFSI salt-based systems. Herein, we used small-angle X-ray scattering/wide-angle X-ray scattering (SAXS/WAXS) and molecular dynamics (MD) simulation to investigate the solvation structure of a series of lithium salts with four different symmetric anions: (bis(fluoro sulfonyl)imide (FSI), bis(trifluoromethane sulfonyl)imide (TFSI), bis(pentafluoroethane sulfonyl) imide (BETI) and bis(nonafluorobutane sulfonyl)imide (BNTI)), which have similar parent structures but different lengths of the fluorocarbon chains. Two competing structures were found in the four lithium salts aqueous solutions: anion solvated structure and anion network. The anion network plays a crucial role in obtaining a stable and enlarged electrochemical window. The d spacing of the anion solvated structure follows a linear correlation with the number of carbons in the fluorocarbon chains and an exponential correlation with the concentrations. We also observed that the transition from one structure to another is predominantly controlled by the salt volume fraction for all imide-based aqueous solutions. This work provides a systematic study of the atomistic scale structures of a series of imide-based lithium salt aqueous solutions that could extend the knowledge of WIS electrolytes.

Salt Formation, to Realize a Good Combination of High Energy and Low Sensitivity of Nitroform-Based Energetic Compounds

Energetic salts constitute an important issue in the field of energetic materials. In this research, the series of energetic salts 5–8 with nitroform structures were obtained by a single-displacement reaction, and their crystal structures were fully characterized by X-ray single-crystal diffraction. As energetic compounds, their energy performance and sensitivity to mechanical stimuli have been explored. These compounds not only exhibit excellent detonation performance (Dv = 8.45–9.13 km s–1 and P = 30.5–37.4 GPa) and extremely high specific impulse (Isp = 262.63–277.42 s) but also show low sensitivity to mechanical stimuli. According to the crystallographic data, the relationship between molecular structure and sensitivity has been explored. The results show that the positive electrostatic potential near the nitroform and the interaction between the intermolecular nitro oxygen atoms (O···O interaction) are significantly reduced after salt formation. In addition, this trend of change is consistent with the sensitivity distribution of these energetic salts (the impact sensitivity decreased from 5 to 15 J and the friction sensitivity decreased from 100 to 240 N). This study not only provides ideas for the molecular design of high-specific-impulse energetic compounds but also reveals the relationship between the structure and sensitivity of nitroform energetic compounds from the perspective of crystallography.

Cationic Effects on the Structural Dynamics of the Metal Ion-Crown Ether Complexes Investigated by Ultrafast Infrared Spectroscopy.

It is usually believed that the binding affinity and selectivity of an alkali metal ion with crown ether are defined by the size matching model. However, the underlying mechanism of the specific host-guest interactions and the structural dynamics of the metal ions confined in the cavity of the crown ethers in the solutions are still not clear. In this report, a series of alkali thiocyanate salts (XSCN; X = Li, Na, K, and Cs) complexed with 18-crown-6 (a typical crown ether) in the chloroform solutions were studied by the polarization-selective infrared pump-probe spectroscopy and the ultrafast two-dimensional infrared (2D IR) spectroscopy. The SCN- counteranions were employed as the local vibrational probe to reveal the specific host-guest interactions in the crown ether complexes. The rotational dynamics and spectral diffusion of SCN- vibration were both measured by ultrafast IR spectroscopy, and it was found that the metal cations hosted by the crown ethers can have a pronounced effect on the rotational dynamics of the counteranions. The reorientational time constants of the SCN- vibration in the complexation follow the order Li+ > Na+ > K+ ≃ Cs+. More importantly, the spectral diffusion dynamics of SCN-, which quantifies the decay of the correlation of the frequency fluctuations in the complexation, was also affected by the metal ions but showed a different order of cationic effect. A detailed analysis of the 2D IR data showed that the spectral diffusion of SCN- counteranion clearly decayed with two different time scales in the complex of 18-crown-6 with K+. The 3-4-fold slowdown in spectral diffusion indicated that the fluctuation of SCN- vibrational transition frequency was strongly affected by the K+ cation due to the geometric constraint imposed by the crown ether. The results should help the researchers to unravel the specific host-guest interactions and further reveal the origination of the binding selectivity of crown ether for metal cations in the condensed phases from the perspective of structural dynamics.

Alkali Metal Dithiocarbamato Carboxylates (DTCCs) – Synthesis, Properties, and Crystal Structures

AbstractA series of alkali metal salts of dithiocarbamate‐substituted carboxylate (DTCC) anions were prepared by reaction of the parent amino acids with carbon disulfide and an alkali metal hydroxide. The target compounds, which were isolated in anhydrous form or as hydrates, were extensively characterized by elemental analyses, IR and NMR spectroscopy, thermal analyses, cyclic voltammetry, and single‐crystal X‐ray diffraction. The isolated compounds are more or less hygroscopic and display a varying dehydratization and decomposition behavior upon heating. The assumed degradation of the DTCC scaffold was found to depend on the substitution pattern as well as on the alkali metal counterion, and covers a range between 200 and 340 °C. In aqueous solution, the DTCC anions show irreversible electrochemical oxidations, where the corresponding redox potentials are governed by the substitution pattern of the nitrogen atom. Single‐crystal structural analyses of sodium and potassium derivatives revealed that these compounds exist as two‐ or three‐dimensional coordination polymers in the solid state, with the alkali‐metal ions adopting typical irregular coordination environments with coordination numbers of six or higher.

Influence of Hydroxyl Group Position and Substitution Pattern of Hydroxybenzoic Acid on the Formation of Molecular Salts with the Antifolate Pyrimethamine

A series of molecular salts of the antimalarial drug pyrimethamine (PYR) with salicylic acid (SA) and its methyl-substituted derivatives 3-methylsalicylic acid (3Me-SA), 4-methylsalicylic acid (4Me-SA), and 5-methylsalicylic acid (5Me-SA) was obtained. Additionally, cocrystallization of PYR with the structural analogues of SA 3-hydroxybenzoic acid (3OH-BA) and 4-hydroxybenzoic acid (4OH-BA) led in the case of 3OH-BA to the formation of a molecular salt, while cocrystallization with 4OH-BA did not lead to the formation of an associate of any kind. In all obtained crystal structures, the carboxylate anion interacts with the protonated at N1 pyrimethamine moiety in a linear fashion through a pair of parallel N–H···O hydrogen bonds forming a cyclic hydrogen-bonded motif. In the crystal structure of PYR-SA as well as in the structures involving methylated derivatives of SA (3Me-SA, 4Me-SA, and 5-Me-SA), a typical PYR-PYR association via a pair of N–H···N bonds between the N(4)H2 amino group of one molecule and the N3 unsubstituted amino atom of the second PYR molecule is observed, a motif that is characteristic of two known PYR polymorphs. On the other hand, in the structure of PYR-3OH-BA, the PYR-PYR connection is realized via a pair of N–H···N bonds between the N(2)H2 amino group of one molecule and the N3 unsubstituted amino atom of the second PYR molecule. In all of the structures, chlorine atoms are involved in C–H···Cl interactions with either the acid molecule or another PYR moiety, while in the structure of PYR-3Me-SA molecules are additionally connected through halogen Cl···Cl interactions. All of the obtained structures were thoroughly characterized by single-crystal X-ray analyses, Hirshfeld analyses, DFT calculations, and thermal analyses (TGA and DSC).

Oxadiazolyl-Pyridinium as Cationic Scaffold for Fluorinated Ionic Liquid Crystals

The synthesis and characterization of a new class of 1,2,4-oxadiazolylpyridinium as a cationic scaffold for fluorinated ionic liquid crystals is herein described. A series of 12 fluorinated heterocyclic salts based on a 1,2,4-oxadiazole moiety, connected through its C(5) or C(3) to an N-alkylpyridinium unit and a perfluoroheptyl chain, differing in the length of the alkyl chain and counterions, has been synthesized. As counterions iodide, bromide and bis(trifluoromethane)sulfonimide have been considered. The synthesis, structure, and liquid crystalline properties of these compounds are discussed on the basis of the tuned structural variables. The thermotropic properties of this series of salts have been investigated by differential scanning calorimetry and polarized optical microscopy. The results showed the existence of an enantiotropic mesomorphic smectic liquid crystalline phase for six bis(trifluoromethane)sulfonimide salts.

A series of stable, metastable and unstable salts of Imatinib with improved solubility

Pharmaceutical salt formation is the most preferred and effective method to enhance the physicochemical properties of APIs. The aim of the study was to design and synthesize a series of new salts to improve the solubility of Imatinib (IM). Two stable salts with malonic acid (S1) and citric acid (S5), one metastable salt with fumaric acid (S2), two unstable salts with citric acid (S3, S4) were obtained for the first time. Single crystal and powder X-ray diffraction, Fourier transform infrared, differential scanning calorimetry, and thermogravimetric analysis were used to characterize the novel salts. The solubility and stability of the solid were also evaluated, and three salts (S1, S2, S5) had a more than 20 folds of solubility and a faster dissolution rate improved as compared to the pure drug in water and pH 6.8 buffer, respectively.