Search

Four mono-substituted N-butylpyridinium salts, 1-butyl-4-dimethylaminopyridinium chloride [b4dmapy]Cl, 1-butyl-4-methylpyridinium bromide [b4mpy]Br, 1-butyl-4-methylpyridinium hexafluorophosphate [b4mpy][PF6], and 1-butyl-3-methylpyridinium hexafluorophosphate [b3mpy][PF6] were synthesized and characterized using single crystal X-ray diffraction. The crystal structures were examined with the intent of identifying ion interactions leading to higher melting points of the halide salts with respect to the [PF6]– salts. The changes in hydrogen bonding, C–H⋅⋅⋅π, and van der Waals interactions have been analyzed with respect to anion, functional groups, and the symmetry of the cation to establish interdependence with the compound's physicochemical properties. It has been observed that the cation–anion interactions are represented by highly directional hydrogen bonds and show strong preference to positions of interaction depending on the anion. The cations of the halide salts show strong tendency towards higher dimensional formations, while those of the [PF6]– salts prefer low dimensional assemblies both being based mainly on the weaker van der Waals interactions. These interactions depend on the shape of the cation but may offer certain structure-ordering rigidity accommodating variable anions. [ABSTRACT FROM AUTHOR]

Utilizing an ionic liquid strategy, we report crystal structures of salts of free anionic nucleobases and base pairs previously studied only computationally and in the gas phase. Reaction of tetrabutylammonium ([N4444]+) or tetrabutylphosphonium ([P4444]+) hydroxide with adenine (HAd) and thymine (HThy) led to hydrated salts of deprotonated adenine, [N4444][Ad]⋅2H2O, and thymine, [P4444][Thy]⋅2H2O, as well as the double salt cocrystal, [P4444]2[Ad][Thy]⋅3H2O⋅2HThy. The cocrystal includes the anionic [Ad-(HThy)] base pair which is a stable formation in the solid state that has previously not even been suggested. It exhibits Watson-Crick connectivity as found in DNA but which is unusual for the free neutral base pairs. The stability of the observed anionic bases and their supramolecular formations and hydrates has also been examined by electronic structure calculations, contributing to more insight into how base pairs can bind when a proton is removed and highlighting mechanisms of stabilization or chemical transformation in the DNA chains. [ABSTRACT FROM AUTHOR]

Ionic liquid forms of biologically active molecules (e.g., active pharmaceutical ingredients or herbicides) are often designed by using weakly interacting, conformationally flexible ions. However, crystalline forms of these molecules involve strong interactions and efficient packing. The salts of biologically active molecules may completely lack the directional supramolecular synthons typically used in crystal engineering, and thus new tools must be developed to control the crystal packing without strong directional interactions and predict their structure–property relationships in advance. The crystal structures of tetrabutylammonium and phosphonium salts of two structurally related, biologically active ions, salicylate and dicamba, show systematic differences from their free acids and metal salts, which are dominated by strong directional interactions. Molecular conformation and the structure of oligomeric ions of acids and their conjugate bases are conserved across multiple structures. The use of flexible, weakly coordinating cations to make salts of high melting biologically active acids can dramatically change melting points based on the size and shape complementarity of the ions and the ability of the cations to enhance anion–anion repulsion. [ABSTRACT FROM AUTHOR]

Bismuth telluride (Bi2Te3) is a well-known thermoelectric material that has a layered crystal structure. Exfoliating Bi2Te3 to produce two-dimensional (2D) nanosheets is extremely important because the exfoliated nanosheets possess unique properties, which can potentially revolutionize several material technologies such as thermoelectrics, heterogeneous catalysts, and infrared detectors. In this work, ionic liquid (IL) 1-butyl-3-methylimidazolium chloride ([C4mim]Cl) is used to exfoliate Bi2Te3 nanoplatelets. In both experiments and in molecular dynamics (MD) simulations, the Bi2Te3 nanoplatelets yield a stable dispersion of 2D nanosheets in the IL solvent, and our MD simulations provide molecular-level insight into the kinetics and thermodynamics of the exfoliation process. An analysis of the dynamics of Bi2Te3 during exfoliation indicates that the relative translation (sliding apart) of adjacent layers caused by IL-induced forces plays an important role in the process. Moreover, an evaluation of the MD trajectories and electrostatic interactions indicates that the [C4mim]+ cation is primarily responsible for initiating Bi2Te3 layer sliding and separation, while the Cl- anion is less active. Overall, our combined experimental and computational investigation highlights the effectiveness of IL-assisted exfoliation, and the underlying molecular-level insights should accelerate the development of future exfoliation techniques for producing 2D chalcogenide materials. [ABSTRACT FROM AUTHOR]

The incorporationof active pharmaceutical ingredients (APIs) intomulticomponent solid forms (such as salts and co-crystals) or liquidforms (such as ionic liquids (ILs) or deep eutectic mixtures) is importantin optimizing the efficacy and delivery of APIs. However, there isa current debate regarding the classification of these multicomponentsystems based on their ionicity which could interfere with their considerationin important applications. Multicomponent systems of intermediateionicity can show a combination of properties, leading to behaviorthat is neither strictly typical of either purely ionic or purelyneutral compounds, nor easily described as intermediate between thetwo. In this perspective, we attempt to illustrate the problems inclassifying multicomponent APIs based on one of two categories bydiscussing selected literature regarding solid and liquid multicomponentAPIs and presenting the crystal structures of some relevant systemsas case studies. It is clear that a focus on restrictive nomenclaturecarries with it the risk that a thorough examination of the physicochemicalproperties of the compounds will be overlooked. [ABSTRACT FROM AUTHOR]

A studyof the first reported crystal structure of anhydrous caffeinehydrochloride reveals irreversible hydration without loss of crystallinityand decomposition with the evolution of HCl gas upon heating. [ABSTRACT FROM AUTHOR]