Molecular Electron Density Distribution and X-Ray Diffraction Patterns of Smectic A Liquid Crystals – A Simulation Study

X-ray diffraction (XRD) is one of the most important methods to assess the long-range translational order in smectic A (SmA) liquid crystals. Nevertheless, the knowledge about the influence of the molecular electron density distribution (MEDD) on the XRD pattern is rather limited because it is not possible to vary the orientational order, the translational order and the MEDD independently in an experiment. We here present a systematic simulation study in which we examine this effect and show that the MEDD indeed has a major impact on the general appearance of the XRD pattern. More specifically, we find that the smectic layer peaks and the intensity ratios thereof strongly depend on the width of the MEDD. The classic approach by Leadbetter et al. to determine the smectic translational order parameter from XRD intensities works if the MEDD is quite narrow. In all other cases the influence of the MEDD has to be taken into account.     

Exchange of Coordinated Solvent During Crystallization of a Metal–Organic Framework Observed by In Situ High‐Energy X‐ray Diffraction

Using time‐resolved monochromatic high energy X‐ray diffraction, we present an in situ study of the solvothermal crystallisation of a new MOF [Yb₂(BDC)₃(DMF)₂]?H₂O (BDC=benzene‐1,4‐dicarboxylate and DMF=N,N‐dimethylformamide) under solvothermal conditions, from mixed water/DMF solvent. Analysis of high resolution powder patterns obtained reveals an evolution of lattice parameters and electron density during the crystallisation process and Rietveld analysis shows that this is due to a gradual topochemical replacement of coordinated solvent molecules. The water initially coordinated to Yb³⁺ is replaced by DMF as the reaction progresses.     

Jahn–Teller Effect in Circulenes: X‐ray Diffraction Study of Coronene and Corannulene Radical Anions

Single‐crystal X‐ray diffraction studies of two polyaromatic radical anions crystallized as sodium salts, namely [Na(DME)₃]⁺[C₂₀H₁₀^?] ( 1 ) and [Na(DME)₃]⁺[C₂₄H₁₂^?] ( 2 ) are reported. This allowed the first structural evaluation of Jahn–Teller (JT) effects for monoreduced circulenes and a comparison between bowl‐shaped corannulene and planar coronene. The C_s and D_2h symmetrical distortions are found to fit the experimental data for C₂₀H₁₀^.? and C₂₄H₁₂^.?, respectively. The continuous symmetry measure (CSM) analysis was carried out to provide a quantitative measure of the JT distortions in 1 and 2 . In addition, the X‐ray crystallographic results were fully supported by DFT calculations.     

Heavy‐Atom Labeled Transmembrane β‐Peptides: Synthesis,CD‐Spectroscopy,and X‐ray Diffraction Studies in Model Lipid Multilayer

Transmembrane β‐peptides are promising candidates for the design of well‐controlled membrane anchors in lipid membranes. Here, we present the synthesis of transmembrane β‐peptides with and without tryptophan anchors, as well as a novel iodine‐labeled d ‐β³‐amino acid. By using one or more of the heavy‐atom labeled amino acids as markers, the orientation of the helical peptide was inferred based on the electron‐density profile determined by X‐ray reflectivity. The β‐peptides were synthesized through manual Fmoc‐based solid‐phase peptide synthesis (SPPS) and reconstituted in unilamellar vesicles forming a right‐handed 3₁₄‐helix secondary structure, as shown by circular dichroism spectroscopy. We then integrated the β‐peptide into solid‐supported membrane stacks and carried out X‐ray reflectivity and grazing incidence small‐angle X‐ray scattering to determine the β‐peptide orientation and its effect on the membrane bilayers. These β‐peptides adopt a well‐ordered transmembrane motif in the solid‐supported model membrane, maintaining the basic structure of the original bilayer with some distinct alterations. Notably, the helical tilt angle, which accommodates the positive hydrophobic mismatch, induces a tilt of the acyl chains. The tilted chains, in turn, lead to a membrane thinning effect.     

Tyrosine‐Based Ionic Liquid Crystals: Switching from a Smectic A to a Columnar Mesophase by Exchange of the Spherical Counterion

Synthetic strategies were developed to prepare l ‐tyrosine‐based ionic liquid crystals with structural variations at the carboxylic and phenolic OH groups as well as the amino functionality. Salt metathesis additionally led to counterion variation. The liquid‐crystalline properties were investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and X‐ray diffraction (WAXS, SAXS). The symmetrical ILC chlorides bearing the same alkyl chain at both the ester and ether but either an acyclic or cyclic guanidinium group displayed enantiotropic SmA₂ mesophases with phase widths of 31–88 K irrespective of the head group. It was particularly the replacement of chloride in the acyclic guanidinium ILC by hexafluorophosphate that induced a phase change from SmA₂ to Col_r. This phase change was attributed to a higher curvature of the interface due to the larger anion, which increased the effective head group cross‐sectional area of the amphiphilic ILC. The unsymmetrical acyclic guanidinium chlorides, bearing a constant C₁₄ ester and variable alkyl chains on the phenolic position, formed enantiotropic SmA₂ phases. The derivative with the largest difference in chain lengths, however, displayed a Col_r phase, resulting from discoid aggregates of the cone‐shaped guanidinium chloride. The results are discussed in terms of the packing parameters, which indicate that the phase behaviour of the thermotropic tyrosine‐based ILCs shows analogies to those of lyotropic liquid crystals.     

A Constrained Disorder Refinement: “Reinvestigation of “Single‐Crystal X‐ray Structure of 1,3‐Dimethylcyclobutadiene” by M. Shatruk and I. V. Alabugin”

Shatruk and Alabugin propose an alternative structural model for the observed electron density that we have attributed to the photochemical formation of 1,3‐dimethylcyclobutadiene in a protective solid crystalline matrix. The main criticism from Shatruk and Alabugin concerns the modeling of the disorder in the calixarene cavity and in particular the neglect of a residual electron density close to the O1 atom. We published (Chem. Eur. J. 2011 , 17, 10021) our opinion concerning this “ignored peak” in the Supporting Information of the paper. The current response to the Correspondence demonstrates that Shatruk and Alabugin have over‐modeled our data by assigning a small electron density peak, which is hardly more than the density corresponding to a hydrogen atom, to an under‐occupied oxygen site, using inappropriate refinement contraints.     

Controlling Nucleation and Crystal Growth of a Distinct Polyoxovanadate Cluster: An In Situ Energy Dispersive X‐ray Diffraction Study under Solvothermal Conditions

The formation of the antimonato polyoxovanadates [V₁₄Sb₈(C₆H₁₅N₃)₄O₄₂(H₂O)] ? 4H₂O ( 1 ), (C₆H₁₇N₃)₂[V₁₅Sb₆(C₆H₁₅N₃)₂O₄₂(H₂O)] ? 2.5H₂O ( 2 ), {C₆H₁₅N₃}₄[V₁₆Sb₄O₄₂] 2H₂O ( 3 ) (C₆H₁₅N₃=1‐(2‐aminoethyl)piperazine, AEP) has been studied under solvothermal conditions by using in situ energy dispersive X‐ray diffraction (EDRXD). The syntheses were performed with an identical ratio for Sb₂O₃ and NH₄VO₃. If the reactions slurries are not stirred during the solvothermal reaction and by applying 70–75 % amine concentration, the products contain all three compounds, whereas 3 is observed at 80 %. Under stirring conditions, variation of the concentration of AEP led to crystallization of the three different compounds at distinct concentrations, that is, 1 is formed at 75 %, 1 and 2 between 75 and 80 % and 3 at 80 %. At an amine concentration of 77.5 %, first reflections of 2 occurred and at later stages, compound 1 started to crystallize. The sample with the lowest number of V^IV species was formed at the lowest amine concentration, whereas crystallization of 3 required the highest concentration. The formation of the compounds occurred without crystalline intermediates and/or precursors. With increasing reaction temperature, the incubation time was significantly reduced.     

Fullerene‐Filled Liquid‐Crystal Stars: A Supramolecular Click Mechanism for the Generation of Tailored Donor–Acceptor Assemblies

Two shape‐persistent star mesogens with oligo(phenylene ethenylene) arms and a phthalocyanine core—one providing free space ( 2 ) and one sterically encumbered by four fullerenes attached through spacers ( 3 )—have been successfully synthesized. In contrast to the smaller discotic derivative 1 , mesogen 2 forms a columnar liquid crystal (LC), which can only be partially aligned without π‐stacking, while 3 is not an LC. Exceptionally, the 1:1 mixture of 2 and 3 forms an alignable columnar LC with strong π‐stacking and quadruply helically organized fullerenes by an unprecedented click process that is similar to a ball detent mechanism. The C₆₀ units also interconnect different columns. This is driven by nanosegregation and space‐filling of the voids with fullerenes. Photophysical studies confirm the presence of a light‐collecting system that generates charge‐separated states in solution and in the solid state, which makes such highly organized materials attractive for the study of future photovoltaic devices.     

Protonation of Ferrocene: A Low‐Temperature X‐ray Diffraction Study of [Cp2FeH](PF6) Reveals an Iron‐Bound Hydrido Ligand

Ferrocene, Cp₂Fe, is quantitatively protonated in a mixture of liquid HF/PF₅ to yield [Cp₂FeH](PF₆), which was characterized by ¹H/¹³C NMR and ⁵⁷Fe Mössbauer spectroscopy as well as single‐crystal X‐ray diffraction analysis. X‐ray diffraction analysis at 100 K revealed a disordered, iron‐coordinated hydrido ligand, which was unambiguously located by aspherical atom refinement at 100 K, and by analyzing the non‐disordered crystal structure at 30 K, revealing a non‐agostic structure.     

ChemInform Abstract: La3BaSi5N9O2:Ce3+ — A Yellow Phosphor with an Unprecedented Tetrahedra Network Structure Investigated by Combination of Electron Microscopy and Synchrotron X‐Ray Diffraction.

Agglomerates of a few μm of the yellow phosphor La₃BaSi₅N₉O₂:Ce³⁺ are obtained by heating a mixture of LaF₃, La(NH₂)₃, BaH₂, Si(NH)₂, and CeF₃ in a radio frequency furnace under N₂ (1600 °C, 10 h; cooling to 900 °C within 44 h).