Recent developments in the chemistry of metal oxopolyazides

Charge frustration in ligand design and functional group transfer

Molecules with different resonance structures of similar importance, such as heterocumulenes and mesoionics, are prominent in many applications of chemistry, including 'click chemistry', photochemistry, switching and sensing. In coordination chemistry, similar chameleonic/schizophrenic entities are referred to as ambidentate/ambiphilic or cooperative ligands. Examples of these had remained, for a long time, limited to a handful of archetypal compounds that were mere curiosities. In this Review, we describe ambiphilicity - or, rather, 'charge frustration' - as a general guiding principle for ligand design and functional group transfer. We first give a historical account of organic zwitterions and discuss their electronic structures and applications. Our discussion then focuses on zwitterionic ligands and their metal complexes, such as those of ylidic and redox-active ligands. Finally, we present new approaches to single-atom transfer using cumulated small molecules and outline emerging areas, such as bond activation and stable donor-acceptor ligand systems for reversible 1e^- chemistry or switching.

Refinement of Copper(II) Azide with 1-Alkyl-5H-tetrazoles: Adaptable Energetic Complexes

A concept for stabilizing highly sensitive and explosive copper(II) azide with 1-N-substituted tetrazoles is described. It was possible to stabilize the system by the use of highly endothermic, nitrogen-rich ligands. The sensitivities of the resulting energetic copper coordination compounds can be tuned further by variation of the alkyl chain of the ligands and by phlegmatization of the complexes with classical additives during the synthesis. It is demonstrated, using the compound based on 1-methyl-5H-tetrazole ([Cu(N3 )2 (MTZ)], 1) that this class of complexes can be applied as a potential replacement for both lead azide (LA) and lead styphnate (LS). The complex was extensively investigated according to its chemical (elemental analysis, single-crystal and powder X-ray diffraction, IR spectroscopy, scanning electron microscopy) and physico-chemical properties (differential thermal analysis, sensitivities towards impact, friction, and electrostatic discharge) compared to pure copper(II) azide.