Preparation of iron(IV) nitridoferrate Ca4FeN4 through azide-mediated oxidation under high-pressure conditions

Transition metal nitrides are an important class of materials with applications as abrasives, semiconductors, superconductors, Li-ion conductors, and thermoelectrics. However, high oxidation states are difficult to attain as the oxidative potential of dinitrogen is limited by its high thermodynamic stability and chemical inertness. Here we present a versatile synthesis route using azide-mediated oxidation under pressure that is used to prepare the highly oxidised ternary nitride Ca4FeN4 containing Fe4+ ions. This nitridometallate features trigonal-planar [FeN3](5-) anions with low-spin Fe4+ and antiferromagnetic ordering below a Neel temperature of 25K, which are characterised by neutron diffraction, Fe-57-Mossbauer and magnetisation measurements. Azide-mediated high-pressure synthesis opens a way to the discovery of highly oxidised nitrides. High-valent metal nitrides are difficult to stabilise due to the high thermodynamic stability and chemical inertness of N-2. Here, the authors employ a large volume press to prepare an iron(IV) nitridoferrate (Ca4FeN4)-N-IV from Fe2N and Ca3N2 via azide-mediated oxidation under high pressure conditions.

Automated summary

Transition metal nitrides are important materials with various applications, but high oxidation states are difficult to achieve due to the stability of dinitrogen. A versatile synthesis route using azide-mediated oxidation under pressure has been developed to prepare highly oxidised ternary nitrides like Ca4FeN4 containing Fe4+ ions. This method opens up new possibilities for the discovery of highly oxidised nitrides.