Supramolecular Recognition Influences Magnetism in [X@HVIV8VV14O54]6− Self‐Assemblies with Symmetry‐Breaking Guest Anions

Mixed‐valence polyoxovanadates(IV/V) have emerged as one of the most intricate class of supramolecular all‐inorganic host species, able to encapsulate a wide variety of smaller guest templates during their self‐assembly formation process. As showcased herein, the incorporation of guests, though governed solely by ultra‐weak electrostatic and van der Waals interactions, can cause drastic effects on the electronic and magnetic characteristics of the shell complex of the polyoxovanadate. We address the question of methodology for the magnetochemical analysis of virtually isostructural {V^IV/V₂₂O₅₄}‐type polyoxoanions of D_2d symmetry enclosing diamagnetic VO₂F₂^? (C_2v), SCN^? (C_∞v), or ClO₄^? (T_d) template anions. These induce different polarization effects related to differences in their geometric structures, symmetry, ion radii, and valence shells, eventually resulting in a supramolecular modulation of magnetic exchange between the V(3d) electrons that are partly delocalized over the {V₂₂O₅₄} shells. We also include the synthesis and characterization of the novel [V^VO₂F₂@HV^IV₈V^V₁₄O₅₄]^6? system that comprises the rarely encountered discrete difluorovanadate anion as a quasi‐isolated guest species.     

Everything you wanted to know about phase and reference frequency in one- and two-dimensional NMR spectroscopy

The fundamental concept of phase discussed in this tutorial aimed at providing students with an explanation of the delays and processing parameters they may find in nuclear magnetic resonance (NMR) pulse programs. We consider the phase of radio-frequency pulses, receiver, and magnetization and how all these parameters are related to phases and offsets of signals in spectra. The impact of the off-resonance effect on the phase of the magnetization is discussed before presenting an overview of how adjustment of the time reference of the free induction decay avoids first-order correction of the phase of spectra. The main objective of this tutorial is to show how the relative phase of a pulse and the receiver can be used to change the reference frequency along direct and indirect dimensions of NMR experiments. Unusual of phase incrementation with non-90° angles will be illustrated on one- and two-dimensional NMR spectra.     

Octaboraneyl Complexes of Nickel: Monomers for Redox-Active Coordination Polymers

Herein, we establish the preparation, characterization, and reactivity of a new diphosphine ligand, 1,2-bis(di(3-dicyclohexylboraneyl)propylphosphino)ethane (P₂B^Cy₄), a scaffold that contains four pendant boranes. An entryway into the coordination chemistry of P₂B^Cy₄ is established by using nickel, providing the octaboraneyl complex [Ni(P₂B^Cy₄)₂]—this species contains a boron-rich secondary coordination sphere that reacts readily with Lewis bases. In the case of 4,4′-bipyridine, an air-sensitive coordination polymer is obtained. Characterization of this material by solid-state NMR and EPR spectroscopy reveals the presence of a charge-transfer polymer, which forms as a function of intramolecular Ni→4,4′-bpy electron transfer (ET), providing an array of oxidized nickel sites and reduced 4,4′-bpy radical anion sites. Notably, the related intermolecular reaction between the model fragments [Ni(dnppe)₂] (dnppe=1,2-bis(di-n-propylphosphino)ethane) and a bis(boraneyl)-protected 4,4′-bpy, provides no ET. Overall, the P₂B^Cy₄ fragment provides a unique opportunity for Lewis base activation, in one case allowing for the facile construction of monomers for incorporation into redox-active macromolecules.     

A Ferrocenyl Kaleidoscope: Slow Interconversion of Six Diastereo‐atropisomers of 2,6‐Di‐tert‐butyl‐9,10‐diferrocenyltriptycene

The title triptycene, 6 , has been isolated as the product of 9,10‐cycloaddition of benzyne to 9,10‐diferrocenyl‐2,6‐di‐tert‐butylanthracene, 5 , whose X‐ray crystal structure is reported. Each ferrocenyl unit in 6 has access to the same three non‐equivalent molecular environments, and their rotations relative to the molecular paddlewheel give rise to six slowly interconverting atropisomers. Their dynamic behaviour in solution is a challenging NMR puzzle that can be successfully solved by taking advantage of the recently described very large diamagnetic anisotropy of the ferrocenyl moiety, together with the C₂ symmetry of particular atropisomers. Application of one‐ and two‐dimensional NMR techniques over a range of temperatures together, with a detailed analysis of the homo‐ and heteronuclear correlations in 6 , resulted in unequivocal mapping of the 99 ¹H and 162 ¹³C positions in the six interconverting systems. Variable‐temperature 2D‐EXSY measurements revealed that, while the stability of the atropisomers is almost identical, they are separated by energy barriers which the ferrocenyls must overcome in the course of their interconversions. The heights of two different rotational barriers have been identified and these experimental findings are in good agreement with DFT calculations.     

Single‐Atom Gold Catalysis in the Context of Developments in Parahydrogen‐Induced Polarization

A highly isolated monoatomic gold catalyst, with single gold atoms dispersed on multiwalled carbon nanotubes (MWCNTs), has been synthesized, characterized, and tested in heterogeneous hydrogenation of 1,3‐butadiene and 1‐butyne with parahydrogen to maximize the polarization level and the contribution of the pairwise hydrogen addition route. The Au/MWCNTs catalyst was found to be active and efficient in pairwise hydrogen addition and the estimated contributions from the pairwise hydrogen addition route are at least an order of magnitude higher than those for supported metal nanoparticle catalysts. Therefore, the use of the highly isolated monoatomic catalysts is very promising for production of hyperpolarized fluids that can be used for the significant enhancement of NMR signals. A mechanism of 1,3‐butadiene hydrogenation with parahydrogen over the highly isolated monoatomic Au/MWCNTs catalyst is also proposed.     

Isotopic separation of lithium ions by capillary zone electrophoresis

Separation of ⁶Li and ⁷Li isotopes by CZE was demonstrated. The BGE contained 5 mM 4‐aminopyridine, 0.9 mM oxalic acid, 0.25 mM CTAB, and 0.25% w/v Tween 20 (рН = 9.2). The running conditions were +25 kV at 30°C with indirect photometric detection at 261 nm. Under optimal experimental conditions, the analysis time was less than 21 min. Separation of Li preparations with mole fraction of ⁶Li ranging from 3.44 up to 90.38% was demonstrated.     

Aqueous and nonaqueous lithium-air batteries enabled by water-stable lithium metal electrodes

The extremely high theoretical energy density of the lithium-oxygen couple makes it very attractive for next-generation battery development. However, there are a number of challenging technical hurdles that must be addressed for Li-Air batteries to become a commercial reality. In this article, we demonstrate how the invention of water-stable, solid electrolyte-protected lithium electrodes solves many of these issues and paves the way for the development of aqueous and nonaqueous Li-Air batteries with unprecedented energy densities. We also show data for fully packaged Li-Air cells that achieve more than 800 Wh/kg.     

Chemical and Electrochemical Lithiation of van der Waals Tetrel-Arsenides

Lithiation of van der Waals tetrel-arsenides, GeAs and SiAs, has been investigated. Electrochemical lithiation demonstrated large initial capacities of over 950 mAh g⁻¹ accompanied by rapid fading over successive cycling in the voltage range 0.01–2 V. Limiting the voltage range to 0.5–2 V achieved more stable cycling, which was attributed to the intercalation process with lower capacities. Ex situ powder X-ray diffraction confirmed complete amorphization of the samples after lithiation, as well as recrystallization of the binary tetrel-arsenide phases after full delithiation in the voltage range 0.5–2 V. Solid-state synthetic methods produce layered phases, in which Si-As or Ge-As layers are separated by Li cations. The first layered compounds in the corresponding ternary systems were discovered, Li_0.9Ge_2.9As_3.1 and Li₃Si₇As₈, which crystallize in the Pbam (No. 55) and P2/m (No. 10) space groups, respectively. Semiconducting layered GeAs and SiAs accommodate the extra charge from Li cations through structural rearrangement in the Si-As or Ge-As layers and eventually by replacement of the tetrel dumbbells with sets of Li atoms. Ge and Si monoarsenides demonstrated high structural flexibility and a mild ability for reversible lithiation.     

Monasnicotinic acid,a novel pyridine alkaloid of the fungus Aspergillus cavernicola: isolation and structure elucidation

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