A Zinc-Mediated Deprotective Annulation Approach to New Polycyclic Heterocycles

A straightforward approach to new polycyclic heterocycles, 1H-benzo[4,5]imidazo[1,2-c][1,3]oxazin-1-ones, is presented. It is based on the ZnCl2-promoted deprotective 6-endo-dig heterocyclization of N-Boc-2-alkynylbenzimidazoles under mild conditions (CH2Cl2, 40 °C for 3 h). The zinc center plays a dual role, as it promotes Boc deprotection (with formation of the tert-butyl carbocation, which can be trapped by substrates bearing a nucleophilic group) and activates the triple bond toward intramolecular nucleophilic attack by the carbamate group. The structure of representative products has been confirmed by X-ray diffraction analysis

New Features in EXPO2007, a Program for Crystal Structure Resolution from Powder Data

New approaches have been introduced in the EXPO2007 program aiming at making easier and straightforward the ab initio crystal structure solution from powder diffraction data. Improvements in space group determination, powder pattern decomposition, least squares Fourier recycling, interpretation of the electron density map have been developed. To manage organic crystal structures a new strategy in direct-space, combining Direct Methods and Simulated Annealing approaches, has been implemented

Organotrifluoroborates as attractive self-assembling systems: the case of bifunctional dipotassium phenylene-1,4-bis(trifluoroborate)

A multitude of non-covalent interactions, investigated by X-ray crystallography and computational chemistry techniques, proved to be responsible of the spontaneous self-assembly of a bis(trifluoroborate) dipotassium salt

NAVIGATING THE COMPLEX SOLID FORM LANDSCAPE OF THE QUERCETIN FLAVONOID MOLECULE

Quercetin, a naturally occurring bioflavonoid substance widely used in the nutraceutical and food industries, exists in various solid forms that can have different physicochemical properties, thus impacting this compound’s performance in various applications. In this work, we will clarify the complex solid-form landscape of this molecule. Two elusive isostructural solvates of quercetin were obtained from ethanol and methanol. The obtained crystals were characterized experimentally, but the crystallographic structure could not be solved due to their high instability. Nevertheless, the desolvated structure resulting from a high-temperature treatment (or prolonged storage at ambient conditions) of both these two labile crystals was characterized and solved via powder X-ray diffraction and solid-state nuclear magnetic resonance (SSNMR). This anhydrous crystal structure was compared with another anhydrous quercetin form obtained in our previous work, indicating that, at least, two different anhydrous polymorphs of quercetin exist. Navigating the solid-form landscape of quercetin is essential to ensure accurate control of the functional properties of food, nutraceutical, or pharmaceutical products containing crystal forms of this substance

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

New frontiers in powder diffraction pattern indexing: the program<i>N-TREOR09</i>

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Magnetoelectric Coupling Springing Up in Molecular Ferroelectric: [N(C2H5)3CH3][FeCl4]

A molecule-based ferroelectric triethylmethylammonium tetrachloroferrate(III) ([N(C2H5)3CH3][FeCl4]) powder was designed as a multifunctional material exhibiting excellent multiple bistability. Prepared by the slow evaporation method at room temperature, the compound crystallizes in the non- centrosymmetric assembly of hexagonal symmetry (P63mc space group) which undergoes a reversible temperature- triggered phase transition pinpointed at 363 K to the centrosymmetric packing within the P63/mmc space group. Aside from the inseparable role of the symmetry-breaking process smoothly unveiled from the X-ray powder diffraction data, a striking change in the dielectric permittivity observed during the paraelectric-to- ferroelectric phase transition directly discloses the bistable dielectric behavior—an exceptionally high increase in the dielectric permittivity of about 360% at 100 kHz across the heating and cooling cycles is direct proof showing the highly desirable stimuli- responsive electric ordering in this improper ferroelectric architecture. Due to the magnetically modulated physical properties resulting in the coupling of magnetic and electric orderings, the flexible assembly of [N(C2H5)3CH3] [FeCl4] could be used to boost the design and development of novel magnetoelectric device

Structure determination of novel ionic co-crystals from powder data: the use of rigid fragments in simulated annealing algorithms

A new approach is presented here for the structural solution of anhydrous and hydrated metal–organic coordination compounds of alkali and alkaline earth metals by using rigid structure fragments in combination with simulated annealing algorithms. We empirically show how this approach minimizes computation time, while allowing us to obtain the correct result. The structures of two novel ionic co-crystals have been solved from powder data with this approach

<i>Ab initio</i>structure determination by powders: recent developments in<i>EXPO2010</i>

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