Mechanical flexibility in single crystals of covalently bound materials is a fascinating and poorly understood phenomenon. We present here the first example of a plastically flexible one‐dimensional (1D) coordination polymer. The compound [Zn(μ‐Cl)2(3,5‐dichloropyridine)2]n is flexible over two crystallographic faces. Remarkably, the single crystal remains intact when bent to 180°. A combination of microscopy, diffraction, and spectroscopic studies have been used to probe the structural response of the crystal lattice to mechanical bending. Deformation of the covalent polymer chains does not appear to be responsible for the observed macroscopic bending. Instead, our results suggest that mechanical bending occurs by displacement of the coordination polymer chains. Based on experimental and theoretical evidence, we propose a new model for mechanical flexibility in 1D coordination polymers. Moreover, our calculations propose a cause of the different mechanical properties of this compound and a structurally similar elastic material.

Water-stable metal–organic frameworks (MOFs) with proton-conducting behavior have attracted great attention as promising materials for proton-exchange membrane fuel cells. Herein, we report the mechanochemical gram-scale synthesis of three new mixed-ligand phosphonate-based MOFs, {Co­(H2PhDPA)­(4,4′-bipy)­(H2O)·2H2O} n (BAM-1), {Fe­(H2PhDPA)­(4,4′-bipy) (H2O)·2H2O} n (BAM-2), and {Cu­(H2PhDPA)­(dpe)2(H2O)2·2H2O} n (BAM-3) [where H2PhDPA = phenylene diphosphonate, 4,4′-bipy = 4,4′-bipyridine, and dpe = 1,2-di­(4-pyridyl)­ethylene]. Single-crystal X-ray diffraction measurements revealed that BAM-1 and BAM-2 are isostructural and possess a three-dimensional (3D) network structure comprising one-dimensional (1D) channels filled with guest water molecules. Instead, BAM-3 displays a 1D network structure extended into a 3D supramolecular structure through hydrogen-bonding and π–π interactions. In all three structures, guest water molecules are interconnected with the uncoordinated acidic hydroxyl groups of the phosphonate moieties and coordinated water molecules by means of extended hydrogen-bonding interactions. BAM-1 and BAM-2 showed a gradual increase in proton conductivity with increasing temperature and reached 4.9 × 10–5 and 4.4 × 10–5 S cm–1 at 90 °C and 98% relative humidity (RH). The highest proton conductivity recorded for BAM-3 was 1.4 × 10–5 S cm–1 at 50 °C and 98% RH. Upon further heating, BAM-3 undergoes dehydration followed by a phase transition to another crystalline form which largely affects its performance. All compounds exhibited a proton hopping (Grotthuss model) mechanism, as suggested by their low activation energy.

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Die mechanische Flexibilität von kovalenten Einkristallen ist ein faszinierendes und wenig verstandenes Phänomen. Wir stellen hier das erste Beispiel eines plastisch flexiblen 1D‐Koordinationspolymers vor. Die Verbindung [Zn(μ‐Cl)2(3,5‐Cl2Py)2]n ist über zwei kristallographische Flächen flexibel und bleibt bemerkenswerterweise auch bei 180° Biegung als Einkristall intakt. Mittels einer Kombination von Mikroskopie‐, Beugungs‐ und spektroskopischen Methoden untersuchen wir die strukturelle Reaktion des Kristallgitters auf mechanische Verformung. Laut den Ergebnissen scheint nicht die Deformation der kovalenten Polymerketten für die beobachtete makroskopische Biegung verantwortlich, sondern eine Verschiebung der Koordinationspolymerketten. Basierend auf experimentellen und theoretischen Erkenntnissen schlagen wir ein neues Modell für die mechanische Flexibilität von 1D‐Koordinationspolymeren vor. Darüber hinaus liefern unsere Berechnungen eine Ursache für die unterschiedlichen mechanischen Eigenschaften dieser Verbindung und eines strukturell ähnlichen elastisches Materials.

Phosphotyrosine residues are essential functional switches in health and disease. Thus, phosphotyrosine biomimetics are crucial for the development of chemical tools and drug molecules. We report here the discovery and investigation of pentafluorophosphato amino acids as novel phosphotyrosine biomimetics. A mild acidic pentafluorination protocol was developed and two PF 5 -amino acids were prepared and employed in peptide synthesis. Their structures, reactivities, and fluorine-specific interactions were studied by NMR and IR spectroscopy, X-ray diffraction, and in bioactivity assays. The mono-anionic PF 5 motif displayed an amphiphilic character binding to hydrophobic surfaces, to water molecules, and to protein-binding sites, exploiting charge and HÀ F-bonding interactions. The novel motifs bind 25-to 30-fold stronger to the phosphotyrosine binding site of the protein tyrosine phosphatase PTP1B than the best current biomimetics, as rationalized by computational methods, including molecular dynamics simulations.

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Dedicated to Professor Josef Breu on the occasion of his 60th birthdayIron-based catalysts have been reported manifold and studied as platinum group metal (PGM) free alternatives for the catalysis of the oxygen reduction reaction (ORR). However, their sustainable preparation by greener synthesis approaches is usually not discussed. In this work, we propose a new method for the sustainable preparation of such catalysts by using a mechanochemical approach, with no solvents and non-toxic chemicals. The materials obtained from low temperature carbonization (700 °C) exhibit considerable and stable catalytic performance for ORR in alkaline medium. A catalyst obtained from iron hydroxide, tryptophan, dicyandiamide, and ammonium nitrate shows the best electrocatalytic performance with an overpotential of 921 mV vs. RHE at 0.1 mA/cm 2 and an electron transfer number of 3.4.

Crystalline porous materials are recognized as promising proton conductors for the proton exchange membrane (PEM) in fuel cell technology owing to their tunable framework structure. However, it is still a challenging bulk synthesis for real-world applications of these materials. Herein, we report the mechanochemical gram-scale synthesis of two isostructural metal hydrogen-bonded organic frameworks (MHOFs) of Co(II) and Ni(II) based on 1-hydroxyethylidenediphosphonic acid (HEDPH 4 ) with 2,2′-bipyridine (2,2′-bipy): Co-(HEDPH 3 ) 2 (2,2′-bipy)•H 2 O (1) and Ni(HEDPH 3 ) 2 (2,2′-bipy)•H 2 O (2). In situ monitoring of the mechanochemical synthesis using different synchrotron-based techniques revealed a one-step mechanism − the starting materials are directly converted to the product. With the existence of extensive hydrogen bonds with amphiprotic uncoordinated phosphonate hydroxyl and oxygen atoms, both frameworks exhibited proton conduction in the range of 10 −4 S cm −1 at room temperature under humid conditions. This study demonstrates the potential of green mechanosynthesis for bulk material preparation of framework-based solid-state proton conductors.