Miguel BP

We prepared a covalent organic framework containing pyrazine (C=N) and phenylimino (−NH−) groups (HPP-COF) as an anode. The robust covalent linkage and the hydrogen bond network between −NH− and H₂O collectively improve the acid-alkaline co-tolerance and promote the rapid conduction of H⁺/OH⁻ by the Grotthuss mechanism. Thus the HPP-COF exhibits superior cycle stability and rate performance in both acidic and alkaline electrolytes.

Abstract

Aqueous rechargeable batteries are prospective candidates for large-scale grid energy storage. However, traditional anode materials applied lack acid-alkali co-tolerance. Herein, we report a covalent organic framework containing pyrazine (C=N) and phenylimino (−NH−) groups (HPP-COF) as a long-cycle and high-rate anode for both acidic and alkaline batteries. The HPP-COF′s robust covalent linkage and the hydrogen bond network between −NH− and water molecules collectively improve the acid-alkaline co-tolerance. More importantly, the hydrogen bond network promotes the rapid transport of H⁺/OH⁻ by the Grotthuss mechanism. As a result, the HPP-COF delivers a superior capacity and cycle stability (66.6 mAh g⁻¹@ 30 A g⁻¹, over 40000 cycles in 1 M H₂SO₄ electrolyte; 91.7 mAh g⁻¹@ 100 A g⁻¹, over 30000 cycles @ 30 A g⁻¹ in 1 M NaOH electrolyte). The work opens a new direction for the structural design and application of COF materials in acidic and alkaline batteries.

A series of C-aryl pyranosides and furanosides were synthesized by ruthenium-catalyzed ortho- and meta-C_Ar−H glycosylation. Mechanistic studies suggest that the key pathway of ortho-C_Ar−H glycosylation involves an oxidative addition/reductive elimination process, while aryl meta-C−H glycosylation is mediated by σ-activation. DFT calculations showed that steric hindrance is responsible for the high stereoselectivity of meta-C_Ar−H glycosylation.

Abstract

C-aryl glycosides are popular basic skeletons in biochemistry and pharmaceutical chemistry. Herein, ruthenium-catalyzed highly stereo- and site-selective ortho- and meta-C_Ar−H glycosylation is described. A series of C-aryl pyranosides and furanosides were synthesized by this method. The strategy showed good substrate scope, and various N-heterocyclic directing groups were compatible with the reaction system. A mechanistic study suggested that the key pathway of ortho-C_Ar−H glycosylation might involve oxidative addition/reduction elimination, whereas aryl meta-C−H glycosylation was mediated by σ-activation. Density functional theory calculations also showed that the high stereoselectivity of meta-C_Ar−H glycosylation was due to steric hindrance.

The coordination chemistry of KrF2 has been limited, in contrast with that of XeF2, which exhibits a far richer coordination chemistry with main‐group and transition‐metal cations. In the present work, reactions of [XeF5][AsF6] with KrF2 in anhydrous HF solvent afforded [F5Xe(FKrF)AsF6] and [F5Xe(FKrF)2AsF6], the first mixed krypton/xenon compounds. X‐ray crystal structures and Raman spectra show the KrF2 ligands and [AsF6]‐ anions are F‐coordinated to the xenon atoms of the [XeF5]+ cations. Quantum‐chemical calculations are consistent with essentially noncovalent ligand‐xenon bonds that may be described in terms of σ‐hole bonding. These complexes significantly extend the XeF2‐KrF2 analogy and the limited chemistry of krypton by introducing a new class of coordination compound in which KrF2 functions as a ligand that coordinates to xenon(VI). The HF solvates, [F5Xe(FH)AsF6] and [F5Xe(FH)SbF6], are also characterized in this study and provide rare examples of HF coordinated to Xe(VI).

Nature, Published online: 07 May 2020; doi:10.1038/s41586-020-2313-x