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Gallium and Indium Alkoxides with Hydride, Cyclopentadienediide and Copper(I) tert-Butoxide as further Components
Gallium hydride stabilized by the base quinonuclidine reacts with acetone under addition of the Ga-H function to the carbon–oxygen double bond yielding (HGa)5(OiPr)8O (1) as isolable compound. (HGa)5(OiPr)8O may be formally split in to four entities of HGa(OiPr)2 and one entity HGaO. The inner atomic skeleton of 1 is a novel Ga5O9 heterocluster with gallium atoms occupying the corners of a distorted trigonal bi-pyramid, an oxygen atom in the center and the remaining alcoholate oxygen atoms bridging eight of the nine edges of the bi-pyramid (X-ray diffraction analysis). Potassium indium alkoxide KIn(OtBu)4 has been used to synthesize several new compounds like In4(OtBu)8(C5H4)2 (2), (py)2CuIn(OtBu)4 (3), and [CuIn(OtBu)4]2 (4) by reaction with TiCl2cp2 (2) and CuCl (3, 4). All compounds were characterized by spectroscopic means and by X-ray structure analyses revealing novel polycyclic structures. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
A Mechanistic Perspective on Plastically Flexible Coordination Polymers
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. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
Hydrogen Bonding Between Ions of Like Charge in Ionic Liquids Characterized by NMR Deuteron Quadrupole Coupling Constants—Comparison with Salt Bridges and Molecular Systems
We present deuteron quadrupole coupling constants (DQCC) for hydroxyl-functionalized ionic liquids (ILs) in the crystalline or glassy states characterizing two types of hydrogen bonding: The regular Coulomb-enhanced hydrogen bonds between cation and anion (c–a), and the unusual hydrogen bonds between cation and cation (c–c), which are present despite repulsive Coulomb forces. We measure these sensitive probes of hydrogen bonding by means of solid-state NMR spectroscopy. The DQCCs of (c–a) ion pairs and (c–c) H-bonds are compared to those of salt bridges in supramolecular complexes and those present in molecular liquids. At low temperatures, the (c–c) species successfully compete with the (c–a) ion pairs and dominate the cluster populations. Equilibrium constants obtained from molecular-dynamics (MD) simulations show van't Hoff behavior with small transition enthalpies between the differently H-bonded species. We show that cationic-cluster formation prevents these ILs from crystallizing. With cooling, the (c–c) hydrogen bonds persist, resulting in supercooling and glass formation. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
A High-Voltage, Dendrite-Free, and Durable Zn–Graphite Battery
The intrinsic advantages of metallic Zn, like high theoretical capacity (820 mAh g−1), high abundance, low toxicity, and high safety have driven the recent booming development of rechargeable Zn batteries. However, the lack of high-voltage electrolyte and cathode materials restricts the cell voltage mostly to below 2 V. Moreover, dendrite formation and the poor rechargeability of the Zn anode hinder the long-term operation of Zn batteries. Here a high-voltage and durable Zn–graphite battery, which is enabled by a LiPF6-containing hybrid electrolyte, is reported. The presence of LiPF6 efficiently suppresses the anodic oxidation of Zn electrolyte and leads to a super-wide electrochemical stability window of 4 V (vs Zn/Zn2+). Both dendrite-free Zn plating/stripping and reversible dual-anion intercalation into the graphite cathode are realized in the hybrid electrolyte. The resultant Zn–graphite battery performs stably at a high voltage of 2.8 V with a record midpoint discharge voltage of 2.2 V. After 2000 cycles at a high charge–discharge rate, high capacity retention of 97.5% is achieved with ≈100% Coulombic efficiency. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Anti-Stokes Stress Sensing: Mechanochemical Activation of Triplet-Triplet Annihilation Photon Upconversion
The development of methods to detect damage in macromolecular materials is of paramount importance to understand their mechanical failure and the structure–property relationships of polymers. Mechanofluorophores are useful and sensitive molecular motifs for this purpose. However, to date, tailoring of their optical properties remains challenging and correlating emission intensity to force induced material damage and the respective events on the molecular level is complicated by intrinsic limitations of fluorescence and its detection techniques. Now, this is tackled by developing the first stress-sensing motif that relies on photon upconversion. By combining the Diels–Alder adduct of a π-extended anthracene with the porphyrin-based triplet sensitizer PtOEP in polymers, triplet–triplet annihilation photon upconversion of green to blue light is mechanochemically activated in solution as well as in the solid state. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
Enzyme Activity by Design: An Artificial Rhodium Hydroformylase for Linear Aldehydes
Artificial metalloenzymes (ArMs) are hybrid catalysts that offer a unique opportunity to combine the superior performance of natural protein structures with the unnatural reactivity of transition-metal catalytic centers. Therefore, they provide the prospect of highly selective and active catalytic chemical conversions for which natural enzymes are unavailable. Herein, we show how by rationally combining robust site-specific phosphine bioconjugation methods and a lipid-binding protein (SCP-2L), an artificial rhodium hydroformylase was developed that displays remarkable activities and selectivities for the biphasic production of long-chain linear aldehydes under benign aqueous conditions. Overall, this study demonstrates that judiciously chosen protein-binding scaffolds can be adapted to obtain metalloenzymes that provide the reactivity of the introduced metal center combined with specifically intended product selectivity.
Unraveling the Light-Activated Reaction Mechanism in a Catalytically Competent Key Intermediate of a Multifunctional Molecular Catalyst for Artificial Photosynthesis
Understanding photodriven multielectron reaction pathways requires the identification and spectroscopic characterization of intermediates and their excited-state dynamics, which is very challenging due to their short lifetimes. To the best of our knowledge, this manuscript reports for the first time on in situ spectroelectrochemistry as an alternative approach to study the excited-state properties of reactive intermediates of photocatalytic cycles. UV/Vis, resonance-Raman, and transient-absorption spectroscopy have been employed to characterize the catalytically competent intermediate [(tbbpy)2RuII(tpphz)RhICp*] of [(tbbpy)2Ru(tpphz)Rh(Cp*)Cl]Cl(PF6)2 (Ru(tpphz)RhCp*), a photocatalyst for the hydrogenation of nicotinamide (NAD-analogue) and proton reduction, generated by electrochemical and chemical reduction. Electronic transitions shifting electron density from the activated catalytic center to the bridging tpphz ligand significantly reduce the catalytic activity upon visible-light irradiation. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
High Blocking Temperature of Magnetization and Giant Coercivity in the Azafullerene Tb 2 @C 79 N with a Single-Electron Terbium–Terbium Bond
The azafullerene Tb 2 @C 79 N is found to be a single-molecule magnet with a high 100-s blocking temperature of magnetization of 24 K and large coercivity. Tb magnetic moments with an easy-axis single-ion magnetic anisotropy are strongly coupled by the unpaired spin of the single-electron Tb−Tb bond. Relaxation of magnetization in Tb 2 @C 79 N below 15 K proceeds via quantum tunneling of magnetization with the characteristic time τ QTM =16 462±1230 s. At higher temperature, relaxation follows the Orbach mechanism with a barrier of 757±4 K, corresponding to the excited states, in which one of the Tb spins is flipped. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
A Stable Manganese Pincer Catalyst for the Selective Dehydrogenation of Methanol
For the first time, structurally defined manganese pincer complexes catalyze the dehydrogenation of aqueous methanol to hydrogen and carbon dioxide, which is a transformation of interest with regard to the implementation of a hydrogen and methanol economy. Excellent long-term stability was demonstrated for the Mn-PNPiPr catalyst, as a turnover of more than 20 000 was reached. In addition to methanol, other important hydrogen carriers were also successfully dehydrogenated.
Covalency-Driven Preservation of Local Charge Densities in a Metal-to-Ligand Charge-Transfer Excited Iron Photosensitizer
Covalency is found to even out charge separation after photo-oxidation of the metal center in the metal-to-ligand charge-transfer state of an iron photosensitizer. The σ-donation ability of the ligands compensates for the loss of iron 3d electronic charge, thereby upholding the initial metal charge density and preserving the local noble-gas configuration. These findings are enabled through element-specific and orbital-selective time-resolved X-ray absorption spectroscopy at the iron L-edge. Thus, valence orbital populations around the central metal are directly accessible. In conjunction with density functional theory we conclude that the picture of a localized charge-separation is inadequate. However, the unpaired spin density provides a suitable representation of the electron–hole pair associated with the electron-transfer process. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.