Itinerant nitrides and salt-like guanidinates – The diversity of solid-state nitrogen chemistry

Recent advances in the chemistry of two peculiar nitrogen-based materials, that is, ternary itinerant iron nitrides and unsubstituted guanidinate salts, are reviewed. Key to their synthesis is the versatile tool ammonia, either as a gas or as a liquid. For metallic nitrides M_xFe_4−xN including transition-metal and main-group elements M, it is of paramount importance to follow an improved ammonolytic reaction for achieving both stable and metastable compounds; in addition, there is a magnetic effect acting on the crystal structure of Ga_xFe_4−xN, and one also finds spin-glass behavior in main-group nitrides (M = Ga, Ge, Sn). The guanidinate review features an oxidation-controlled low-temperature synthesis of Yb salts, the first magnetic guanidinates, and the doubly-deprotonated guanidinates; the latter represent the all-nitrogen analogues of the ubiquitous carbonates. The covered guanidinates adopt the compositions MCN₃H₄, M(CN₃H₄)₂, M(CN₃H₄)₃ and MC(NH)₃ (M = Li–Cs, Sr, Eu, Yb). We also cover the application of first-principles calculations at all levels to gain a deeper understanding of the studied materials.