Novel contributions to the solid-state chemistry of diazenides

In solid-state chemistry, the existence of homonuclear diatomic nitrogen anions has proven existence only very recently, although the latter represent a common and well-characterized structural motif in biological and synthetic chemistry. Thereby, high-pressure/high-temperature (HP/HT) syntheses starting from the elements and using specialized equipments have introduced binary diazenides (M = Sr, Ba, La) and pernitrides (M = Os, Ir, Pd, Pt) with MN2 stoichiometry consisting of [N2]2– and [N2]4– ions, respectively. Nevertheless, synthesis and characterization of only a handful of examples of both materials classes since their identification in 2001 is quite surprising. Within this context, it is likewise remarkable that solids with isoelectronic, homonuclear diatomic ions consisting of elements to the left (carbon) and to the right (oxygen) of nitrogen in the periodic table have already been synthesized and characterized decades ago. Introducing the approach of controlled thermal decomposition of ionic azides of Group I and II metals in a multianvil device at extreme conditions resulted in a renaissance of homonuclear diatomic nitrogen chemistry. This high-pressure route proved as excellent tool for the synthesis of hitherto unknown binary and even ternary materials with homonuclear diatomic nitrogen anions. However, compared to the classification of valencies in bound N2 entities observed in bioinorganic or metal-organic chemistry, their adequate description in solid-state chemistry is hindered due to, for example potential metallicity in such compounds. Nevertheless, by the use of a variety of complementary experimental and theoretical methods, such as powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), density functional theory (DFT), infrared spectroscopy (FTIR), nuclear magnetic and electron spin resonance spectroscopy (NMR, ESR), the identification of [N2]2- anions in solid-state compounds was possible