A series of energetic metal pentazolate hydrates

Metal complexes of the pentazole anion exhibit multiple coordination modes, through ionic, covalent and hydrogen-bonding interactions, and good thermal stability with onset decomposition temperatures greater than 100 °C. Stable nitrogen noose Polynitrogen compounds can decompose to N 2 with an extraordinarily large energy release, which makes them promising candidate materials for explosives but difficult to produce in a stable form. Compounds containing five-membered all-nitrogen rings have attracted particular interest in the search for a stable polynitrogen molecule. Yuangang Xu et al . report five metal complexes containing the pentazole anion, cyclo --N 5 − , four of which exhibit good thermal stability and a range of different bonding interactions for stabilization. Given their energetic properties and stability, and the adaptability of the cyclo -N 5 − species in terms of its bonding interactions, these complexes might lead to the development of a new class of high-energy-density materials and of other unusual polynitrogen complexes. Singly or doubly bonded polynitrogen compounds can decompose to dinitrogen (N 2 ) with an extremely large energy release. This makes them attractive as potential explosives or propellants 1 , 2 , 3 , but also challenging to produce in a stable form. Polynitrogen materials containing nitrogen as the only element exist in the form of high-pressure polymeric phases 4 , 5 , 6 , but under ambient conditions even metastability is realized only in the presence of other elements that provide stabilization. An early example is the molecule phenylpentazole, with a five-membered all-nitrogen ring, which was first reported in the 1900s 7 and characterized in the 1950s 8 , 9 . Salts containing the azide anion (N 3 − ) 10 , 11 , 12 or pentazenium cation (N 5 + ) 13 are also known, with compounds containing the pentazole anion, cyclo -N 5 − , a more recent addition 14 , 15 , 16 . Very recently, a bulk material containing this species was reported 17 and then used to prepare the first example of a solid-state metal–N 5 complex 18 . Here we report the synthesis and characterization of five metal pentazolate hydrate complexes [Na(H 2 O)(N 5 )]·2H 2 O, [M(H 2 O) 4 (N 5 ) 2 ]·4H 2 O (M = Mn, Fe and Co) and [Mg(H 2 O) 6 (N 5 ) 2 ]·4H 2 O that, with the exception of the Co complex, exhibit good thermal stability with onset decomposition temperatures greater than 100 °C. For this series we find that the N 5 − ion can coordinate to the metal c