Saddles as rotational locks within shape-assisted self-assembled nanosheets

Two-dimensional (2D) materials are a key target for many applications in the modern day. Self-assembly is one approach that can bring us closer to this goal, which usually relies upon strong, directional interactions instead of covalent bonds. Control over less directional forces is more challenging and usually does not result in as well-defined materials. Explicitly incorporating topography into the design as a guiding effect to enhance the interacting forces can help to form highly ordered structures. Herein, we show the process of shape-assisted self-assembly to be consistent across a range of derivatives that highlights the restriction of rotational motion and is verified using a diverse combination of solid state analyses. A molecular curvature governed angle distribution nurtures monomers into loose columns that then arrange to form 2D structures with long-range order observed in both crystalline and soft materials. These features strengthen the idea that shape becomes an important design principle leading towards precise molecular self-assembly and the inception of new materials

Electron crystallography and dedicated electron-diffraction instrumentation

Electron diffraction (known also as ED, 3D ED or microED) is gaining momentum in science and industry. The application of electron diffraction in performing nano-crystallography on crystals smaller than 1 µm is a disruptive technology that is opening up fascinating new perspectives for a wide variety of compounds required in the fields of chemical, pharmaceutical and advanced materials research. Electron diffraction enables the characterization of solid compounds complementary to neutron, powder X-ray and single-crystal X-ray diffraction, as it has the unique capability to measure nanometre-sized crystals. The recent introduction of dedicated instrumentation to perform ED experiments is a key aspect of the continued growth and success of this technology. In addition to the ultra-high-speed hybrid-pixel detectors enabling ED data collection in continuous rotation mode, a high-precision goniometer and horizontal layout have been determined as essential features of an electron diffractometer, both of which are embodied in the Eldico ED-1. Four examples of data collected on an Eldico ED-1 are showcased to demonstrate the potential and advantages of a dedicated electron diffractometer, covering selected applications and challenges of electron diffraction: (i) multiple reciprocal lattices, (ii) absolute structure of a chiral compound, and (iii) R-values achieved by kinematic refinement comparable to X-ray data

3D electron diffraction analysis of a novel, mechanochemically synthesized supramolecular organic framework based on tetra­kis-4-(4-pyridyl)phenyl­methane

Tetrakis-4-(4-pyridyl)phenylmethane (TPPM) is a tetrahedral rigid molecule that crystallizes forming a dynamically responsive supramolecular organic framework (SOF). When exposed to different stimuli, this supramolecular network can reversibly switch from an empty to a filled solvated solid phase. This article describes a novel expanded form of a TPPM-based SOF that has been mechanochemically synthesized and whose crystal structure has been determined by 3D electron diffraction analysis using a novel electron diffractometer

Synthesis and Application of Strong Brønsted Acids Generated from the Lewis Acid Al(OR^F)₃ and an Alcohol

The strong neutral Brønsted acids [(R)­OH→Al­(OC­(CF₃)₃)₃] (R = −C­(CF₃)₃ (<b>1</b>), −C₆F₅ (<b>2</b>), (−)-menthyl (<b>3</b>)) were synthesized by complexation of perfluoro <i>tert</i>-butyl alcohol, pentafluorophenol, and (−)-menthol with the Lewis superacid Al­(OC­(CF₃)₃)₃. The 1:1 composition of the compounds was proven by NMR (except for compound <b>2</b>), IR, and partially Raman spectroscopy and X-ray crystallography. Of the structures, <b>2</b> crystallized with a coordinated toluene molecule, which might be seen as a frozen intermediate or prestep to form the classical Wheland complex of protonated toluene. This interaction was calculated to be exothermic by 32 (no dispersion) or 88 kJ mol^–1 (Grimmes D3 dispersion correction included @ RI-BP86/SV­(P)). <b>1</b> proved suitable to protonate mesitylene and Et₂O, giving the acidic cationic Brønsted acids [H­(C₆H₃(CH₃)₃)]⁺ (<b>4b</b>) and [H­(OEt₂)₂]⁺ (<b>5</b>) with the respective weakly coordinating anion [Al­(OC­(CF₃)₃)₄]⁻. In dichloromethane solution <b>4b</b> decomposes at room temperature, leaving the room-temperature-stable salt [H­(C₆H₃(CH₃)₃)]⁺[((CF₃)₃CO)₃Al–F–Al­(OC­(CF₃)₃)₃]⁻ (<b>4a</b>; XRD). The acidities reached with <b>4</b> and <b>5</b> are discussed in terms of our recently introduced absolute Brønsted acidity scale. The absolute chemical potentials of a 0.001 M solution of protonated mesitylene and Et₂O amount to −944 and −1015 kJ mol^–1 orin terms of absolute pH_abs valuesto 165 and 178 and thus are at the threshold of superacidity of −975 kJ mol^–1 or pH_abs of 171

Synthesis and Application of Strong Brønsted Acids Generated from the Lewis Acid Al(OR^F)₃ and an Alcohol

The strong neutral Brønsted acids [(R)­OH→Al­(OC­(CF₃)₃)₃] (R = −C­(CF₃)₃ (<b>1</b>), −C₆F₅ (<b>2</b>), (−)-menthyl (<b>3</b>)) were synthesized by complexation of perfluoro <i>tert</i>-butyl alcohol, pentafluorophenol, and (−)-menthol with the Lewis superacid Al­(OC­(CF₃)₃)₃. The 1:1 composition of the compounds was proven by NMR (except for compound <b>2</b>), IR, and partially Raman spectroscopy and X-ray crystallography. Of the structures, <b>2</b> crystallized with a coordinated toluene molecule, which might be seen as a frozen intermediate or prestep to form the classical Wheland complex of protonated toluene. This interaction was calculated to be exothermic by 32 (no dispersion) or 88 kJ mol^–1 (Grimmes D3 dispersion correction included @ RI-BP86/SV­(P)). <b>1</b> proved suitable to protonate mesitylene and Et₂O, giving the acidic cationic Brønsted acids [H­(C₆H₃(CH₃)₃)]⁺ (<b>4b</b>) and [H­(OEt₂)₂]⁺ (<b>5</b>) with the respective weakly coordinating anion [Al­(OC­(CF₃)₃)₄]⁻. In dichloromethane solution <b>4b</b> decomposes at room temperature, leaving the room-temperature-stable salt [H­(C₆H₃(CH₃)₃)]⁺[((CF₃)₃CO)₃Al–F–Al­(OC­(CF₃)₃)₃]⁻ (<b>4a</b>; XRD). The acidities reached with <b>4</b> and <b>5</b> are discussed in terms of our recently introduced absolute Brønsted acidity scale. The absolute chemical potentials of a 0.001 M solution of protonated mesitylene and Et₂O amount to −944 and −1015 kJ mol^–1 orin terms of absolute pH_abs valuesto 165 and 178 and thus are at the threshold of superacidity of −975 kJ mol^–1 or pH_abs of 171

Saddles as rotational locks within shape-assisted self-assembled nanosheets

Two-dimensional (2D) materials are a key target for many applications in the modern day. Self-assembly is one approach that can bring us closer to this goal, which usually relies upon strong, directional interactions instead of covalent bonds. Control over less directional forces is more challenging and usually does not result in as well-defined materials. Explicitly incorporating topography into the design as a guiding effect to enhance the interacting forces can help to form highly ordered structures. Herein, we show the process of shape-assisted self-assembly to be consistent across a range of derivatives that highlights the restriction of rotational motion. A shape governed angle distribution nurtures monomers into loose columns that then arrange to form 2D structures with long-range order observed in both crystalline and soft materials. These features strengthen the idea that shape becomes an important design principle leading towards precise molecular self-assembly and the inception of new materials