Electron Density of Two Bioactive Oligocyclic Indole and Oxindole Derivatives Obtained from Low‐Order X‐Ray Data and Invariom Application

For two indole and oxindole bioactive molecules, low‐order room‐temperature X‐ray data were used to generate aspherical electron density (ED) distributions by application of the invariom formalism. An analysis of the ED using the quantum theory of atoms in molecules (QTAIM) was carried out, which allowed for quantitatively examining bond orders and charge separations in various parts of the molecules. The inspection of electrostatic potentials (ESPs) and Hirshfeld surfaces provided additional information on the intermolecular interactions. Thus, reactive regions of the molecules could be identified, covalent and electrostatic contributions to interactions could be visualized, and the forces causing the crystal packing scheme could be rationalized. As the used invariom formalism needs no extra experimental effort compared to routine X‐ray analysis, its wide application is recommended because it delivers information far beyond the normally obtained steric properties. In this way, complementary contributions to drug design can be given as is demonstrated for indoles in this study, which are involved in the metabolism of plants and animals as well as in cancer therapy.     

Probing systematic errors in experimental charge density by multipole and invariom modeling: a twinned crystal of 1,10-phenanthroline hydrate

The modeling of experimental electron density in a twinned crystal of 1,10-phenanthroline hydrate within an invariom approach revealed its another advantage for charge density studies, which is assessing the reliability of chemically relevant information provided by a conventional multipole refinement against high-resolution X-ray diffraction data.     

Subsurface Space‐Charge Dopant Segregation to Compensate Surface Excess Charge in a Perovskite Oxide

Since the first prediction by Frenkel, many follow‐up studies have been carried out to show the presence of subsurface space‐charge layers having the opposite sign to that of the excess charge at the surface, producing overall neutrality in ionic crystals. However, no precise experimental evidence demonstrating how the aliovalent solutes segregate in the space‐charge region beneath the surface has been provided over the past several decades. By utilizing atomic‐scale imaging and chemical probing in a perovskite oxide, the origin of the surface excess charge at the topmost surface and the position of segregated dopants in the space‐charge region is precisely determined. The impact of the space‐charge contribution to the dopant distribution near the surface in oxide crystals is explored.     

First Examples of de Vries‐like Smectic A to Smectic C Phase Transitions in Ionic Liquid Crystals

In ionic liquid crystals, the orthogonal smectic A phase is the most common phase whereas the tilted smectic C phase is rather rare. We present a new study with five novel ionic liquid crystals exhibiting both a smectic A as well as the rare smectic C phase. Two of them have a phenylpyrimidine core whereas the other three are imidazolium azobenzenes. Their phase sequences and tilt angles were studied by polarizing microscopy and their temperature‐dependent layer spacing as well as their translational and orientational order parameters were studied by X‐ray diffraction. The X‐ray tilt angles derived from X‐ray studies of the layer contraction and the optically measured tilt angles of the five ionic liquid crystals were compared to obtain their de Vries character. Four of our five mesogens turned out to show de Vries‐like behavior with a layer shrinkage that is far less than that expected for conventional materials. These materials can thus be considered as the first de Vries‐type materials among ionic liquid crystals.     

Invariom‐model refinement and Hirshfeld surface analysis of well‐ordered solvent‐free dibenzo‐21‐crown‐7

Crown ethers and their supramolecular derivatives are well‐known chelators and scavengers for a variety of cations, most notably heavier alkali and alkaline‐earth ions. Although they are widely used in synthetic chemistry, available crystal structures of uncoordinated and solvent‐free crown ethers regularly suffer from disorder. In this study, we present the X‐ray crystal structure analysis of well‐ordered solvent‐free crystals of dibenzo‐21‐crown‐7 (systematic name: dibenzo[b ,k ]‐1,4,7,10,13,16,19‐heptaoxacycloheneicosa‐2,11‐diene, C₂₂H₂₈O₇). Because of the quality of the crystal and diffraction data, we have chosen invarioms, in addition to standard independent spherical atoms, for modelling and briefly discuss the different refinement results. The electrostatic potential, which is directly deducible from the invariom model, and the Hirshfeld surface are analysed and complemented with interaction‐energy computations to characterize intermolecular contacts. The boat‐like molecules stack along the a axis and are arranged as dimers of chains, which assemble as rows to form a three‐dimensional structure. Dispersive C—H…H—C and C—H…π interactions dominate, but nonclassical hydrogen bonds are present and reflect the overall rather weak electrostatic influence. A fingerprint plot of the Hirshfeld surface summarizes and visualizes the intermolecular interactions. The insight gained into the crystal structure of dibenzo‐21‐crown‐7 not only demonstrates the power of invariom refinement, Hirshfeld surface analysis and interaction‐energy computation, but also hints at favourable conditions for crystallizing solvent‐free crown ethers.     

Invariom‐model refinement of l‐valinol

The structure of l ‐valinol [(S)‐(+)‐2‐amino‐3‐methyl­butan‐1‐ol or hydroxy­lated l ‐valine], C₅H₁₃NO, has been determined at 100 K by single‐crystal X‐ray diffraction. The independent atom model geometry, Flack parameter and figures of merit are compared with results from an invariom structure refinement. The latter provides H‐atom positions free of independent atom model bias and therefore yields a more accurate hydrogen‐bond pattern, and the geometry from invariom refinement shows an improved agreement with results from a quantum chemical geometry optimization.     

Reactivity of molecular oxygen on the surface of ionic crystals

A possibility of multiplicity change for ground‐state molecular oxygen adsorbed on the surface of regular and doped broad‐gap ionic crystals was considered in the framework of cluster approximation by using SCF MO LCAO quantum chemical methods [semiempirical INDO approximation and ab initio calculation with the 6‐311G** basis set taking into account the correlation effects on the level of second‐order Meller–Plesset perturbation theory (MP2)]. The formation energetics of cyclic products of addition reactions of dioxygen in different multiplet states to furan and cis‐butadiene in the gas phase and on the surface of ionic crystals was considered. (These reactions are typical for the O₂ singlet state in the gas phase.) It is shown that the presence of sites with high effective charge on the crystal surface can result in a situation not requiring, as in the gas phase, multiplicity change in the transition of a system from an initial to the final state, which can significantly affect the kinetic parameters of the reactions. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Experimental and experimental-theoretical topological characteristics of the electron density distribution in the crystal of NCN-(2-pyridinecarbonitrile)-(3,6-di-tert-butylcatecholato)triphenylantimony(v)

Russian Chemical Bulletin - Experimental and experimental-theoretical studies (the invariom approach, whole-molecule aspherical scattering factors) of the electron density distribution were carried...     

Nanoscale polyoxometalate‐based inorganic/organic hybrids

The latest advances in the area of polyoxometalate (POM)‐based inorganic/organic hybrid materials prepared by self‐assembly, covalent modification, and supramolecular interactions are presented. This Review is composed of five sections and documents the effect of organic cations on the formation of novel POMs, surfactant encapsulated POM‐based hybrids, polymeric POM/organic hybrid materials, POMs‐containing ionic crystals, and covalently functionalized POMs. In addition to their role in the charge‐balancing, of anionic POMs, the crucial role of organic cations in the formation and functionalization of POM‐based hybrid materials is discussed. DOI 10.1002/tcr.201100002     

Observation of Charge Separation and Space‐Charge Region in Single‐Crystal P3HT/C60 Heterojunction Nanowires

We directly observed charge separation and a space‐charge region in an organic single‐crystal p–n heterojunction nanowire, by means of scanning photocurrent microscopy. The axial p–n heterojunction nanowire had a well‐defined planar junction, consisted of P3HT (p‐type) and C₆₀ (n‐type) single crystals and was fabricated by means of the recently developed inkjet‐assisted nanotransfer printing technique. The depletion region formed at the p–n junction was directly observed by exploring the spatial distribution of photogenerated carriers along the heterojunction nanowire under various applied bias voltages. Our study provides a facile approach toward the precise characterization of charge transport in organic heterojunction systems as well as the design of efficient nanoscale organic optoelectronic devices.     

How Many Phosphoric Acid Units Are Required to Ensure Uniform Occlusion of Sterically Stabilized Nanoparticles within Calcite?

Polymerization‐induced self‐assembly (PISA) mediated by reversible addition–fragmentation chain transfer (RAFT) polymerization offers a platform technology for the efficient and versatile synthesis of well‐defined sterically stabilized block copolymer nanoparticles. Herein we synthesize a series of such nanoparticles with tunable anionic charge density within the stabilizer chains, which are prepared via statistical copolymerization of anionic 2‐(phosphonooxy)ethyl methacrylate (P) with non‐ionic glycerol monomethacrylate (G). Systematic variation of the P/G molar ratio enables elucidation of the minimum number of phosphate groups per copolymer chain required to promote nanoparticle occlusion within a model inorganic crystal (calcite). Moreover, the extent of nanoparticle occlusion correlates strongly with the phosphate content of the steric stabilizer chains. This study is the first to examine the effect of systemically varying the anionic charge density of nanoparticles on their occlusion efficiency and sheds new light on maximizing the loading of guest nanoparticles within calcite host crystals.     

Electric Double‐Layer Capacitor Based on an Ionic Clathrate Hydrate

Herein, we suggest a new approach to an electric double‐layer capacitor (EDLC) that is based on a proton‐conducting ionic clathrate hydrate (ICH). The ice‐like structures of clathrate hydrates, which are comprised of host water molecules and guest ions, make them suitable for applications in EDLC electrolytes, owing to their high proton conductivities and thermal stabilities. The carbon materials in the ICH Me₄NOH ? 5 H₂O show a high specific capacitance, reversible charge–discharge behavior, and a long cycle life. The ionic‐hydrate complex provides the following advantages in comparison with conventional aqueous and polymer electrolytes: 1) The ICH does not cause leakage problems under normal EDLC operating conditions. 2) The hydrate material can be utilized itself, without requiring any pre‐treatments or activation for proton conduction, thus shortening the preparation procedure of the EDLC. 3) The crystallization of the ICH makes it possible to tailor practical EDLC dimensions because of its fluidity as a liquid hydrate. 4) The hydrate solid electrolyte exhibits more‐favorable electrochemical stability than aqueous and polymer electrolytes. Therefore, ICH materials are expected to find practical applications in versatile energy devices that incorporate electrochemical systems.     

A new QM/MM method oriented to the study of ionic liquids

The interest on room temperature ionic liquids has grown in the last decades because of their use as all‐purpose solvent and their low environmental impact. In the present work, a new theoretical procedure is developed to study pure ionic liquids within the framework of the quantum mechanics/molecular mechanics method. Each type of ion (cation or anion) is considered as an independent entity quantum mechanically described that follows a differentiated path in the liquid. The method permits, through an iterative procedure, the full coupling between the polarized charge distribution of the ions and the liquid structure around them. The procedure has been tested with 1‐ethyl‐3‐methylimidazolium tetrafluoroborate. It was found that, similar to non‐polar liquids and as a consequence of the low value of the reaction field, the cation and anion charge distributions are hardly polarized by the rest of molecules in the liquid. Their structure is characterized by an alternance between anion and cation shells as evidenced by the coincidence of the first maximum of the anion–anion and cation–cation radial distribution functions with the first minimum of the anion‐cation. Some degree of stacking between the cations is also found. © 2015 Wiley Periodicals, Inc.     

Not Guilty on Every Count: The “Non‐Innocent” Nitrosyl Ligand in the Framework of IUPAC′s Oxidation‐State Formalism

Nitrosyl–metal bonding relies on the two interactions between the pair of N–O‐π* and two of the metal's d orbitals. These (back)bonds are largely covalent, which makes their allocation in the course of an oxidation‐state determination ambiguous. However, apart from M‐N‐O‐angle or net‐charge considerations, IUPAC′s “ionic approximation” is a useful tool to reliably classify nitrosyl metal complexes in an orbital‐centered approach.     

Superfluorinated Ionic Liquid Crystals Based on Supramolecular,Halogen‐Bonded Anions

Unconventional ionic liquid crystals in which the liquid crystallinity is enabled by halogen‐bonded supramolecular anions [C_nF_{2 n+1}‐I???I???I‐C_nF_{2 n+1}]^? are reported. The material system is unique in many ways, demonstrating for the first time 1) ionic, halogen‐bonded liquid crystals, and 2) imidazolium‐based ionic liquid crystals in which the occurrence of liquid crystallinity is not driven by the alkyl chains of the cation.     

Superfluorinated Ionic Liquid Crystals Based on Supramolecular,Halogen‐Bonded Anions

Unconventional ionic liquid crystals in which the liquid crystallinity is enabled by halogen‐bonded supramolecular anions [C_nF_{2 n+1}‐I⋅⋅⋅I⋅⋅⋅I‐C_nF_{2 n+1}]⁻ are reported. The material system is unique in many ways, demonstrating for the first time 1) ionic, halogen‐bonded liquid crystals, and 2) imidazolium‐based ionic liquid crystals in which the occurrence of liquid crystallinity is not driven by the alkyl chains of the cation.     

Quantum chemical investigation of lanthanum doping effects in tetragonal and rhombohedral PZT materials

Structural and electronic properties of lead–zirconate–titanate (PZT) materials doped with a lanthanum (La) impurity are studied using a quantum‐chemical approach based on the Hartree–Fock theory. Performed geometry optimization in the defective crystals shows that the atomic movements are predominantly outward with respect to the impurity position. It is found that the La impurity enhances a covalent character in the chemical bonding between the Ti and O atoms, as well as the Zr and O atoms situated in the neighborhood of the defect despite the fact that the La‐O interaction remains purely ionic. The occurrence of local energy levels within the band gap of the material is analyzed in light of the available experimental data on La concentration influence upon dielectric and piezoelectric properties in these crystals. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Chemischer Transport fester Lösungen. 22 [1] Beschreibung des Chemischen Transports im System ZnS/ZnSe

Studies on the Chemical Vapor Transport in the System ZnS/ZnSe By means of chemical transport reactions homogeneous ionic mixed crystals with well defined compositions can be prepared in a simple way. This is shown at the example of ZnS/ZnSe‐mixed crystals. ZnS_1?xSe_x‐mixed crystals can be prepared by chemical vapour transport in the temperature gradient 1000 → 900 °C using iodine as transport agent. A thermodynamic model is presented to calculate the thermodynamic stability of ionic mixed phases and possible enrichment effects during the vapor transport. The results are compared with experimental fundings and well known transport models.