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

Abstract

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 25 K, which are characterised by neutron diffraction, 57Fe-Mössbauer and magnetisation measurements. Azide-mediated high-pressure synthesis opens a way to the discovery of highly oxidised nitrides.

Preparation of Bulk‐Phase Nitride Perovskite LaReN3 and Topotactic Reduction to LaNiO2‐Type LaReN2

“…For example, N 2 ‐loaded diamond‐anvil‐cells (DAC) were used for the preparation of noble metal nitrides, pernitrides, polynitrides and pentazolate salts, but with DACs the sample volume is very small and investigations are usually limited to binary phases [20–22] . In situ nitridation methods using large‐volume‐presses are far less studied, but recently bulk‐phases of rocksalt‐type Mg 0.4 Fe 0.6 N and a novel highly oxidized iron(IV) nitride, Ca 4 FeN 4 , were reported using methods based on solid sodium azide [23–25] . Here we report that the nitride perovskite LaReN 3 can be prepared by this method, starting from commercial NaN 3 , LaN and Re metal.…”

“…[20][21][22] In situ nitridation methods using large-volume-presses are far less studied, but recently bulkphases of rocksalt-type Mg 0.4 Fe 0.6 N and a novel highly oxidized iron(IV) nitride, Ca 4 FeN 4 , were reported using methods based on solid sodium azide. [23][24][25] Here we report that the nitride perovskite LaReN 3 can be prepared by this method, starting from commercial NaN 3 , LaN and Re metal. We have also synthesised and characterised the layered LaNiO 2 -type LaReN 2 via a post-synthetic topotactic reduction of LaReN 3 during which an intermediate phase that is probably LaReN 2.5 is also observed.…”

Low-dimensional magnetism in calcium nitridonickelate(ii) Ca2NiN2

“…[27][28][29][30] Much less work has been done in multianvil largevolume presses but recently it was discovered that sodium azide can be used as a N 2 source, as demonstrated in the syntheses of rocksalt-type Mg 0.4 Fe 0.6 N and the highly oxidized nitridoferrate(IV) Ca 4 FeN 4 . [31][32][33] Large-volume-presses offer the advantage over DACs that larger sample quantities for physical properties measurements can be prepared and multinary systems can more easily be studied.…”

“…There was no evidence of a Ca/Na mixed position through initial Rietveld refinement, consistent with Ca 4 FeN 4 , where the absence of Na incorporation was verified through Mössbauer and Please do not adjust margins Please do not adjust margins magnetization measurements. 32 The excess Ca 3 N 2 might have formed an amorphous byproduct as the powder pattern showed a heightened background at low Q. Ni in linear coordination and simple σ-bonding adapted from literature. 11 The crystal structure of Ca 2 NiN 2 (space group I4/mmm, Z = 2, a = 3.57206(2), c = 12.19453(10) Å, V = 155.719(5) Å 3 ) was determined from powder diffraction data by charge flipping in P n2 and subsequent refinement (Figure 1a) in I4/mmm.…”

“…1c) are equal in the equatorial plane and both Ca-N distances (Figure 1d) are in the range observed in similar compounds like CaNiN, Ca 2 ZnN 2 , Ca 2 FeN 2 , Ca 4 FeN 4 , Ca 5 Co 2 N 4 , and Ca 3 N 2 (d Ca-N = 2.40-2.82 Å). 13,32,36,[41][42][43] The Ni-N distance observed in Ca 2 NiN 2 is smaller than in compounds containing infinite N-Ni-N chains like CaNi I N (d Ni-N = 1.792(1) Å) and BaNi I N (d Ni-N = 1.8281(1), 1.781(1) Å), which is probably owed to the higher oxidation state of Ni and the terminal Ni-N bonds. 13,17 Bond valence sum (BVS) calculations were performed for Ca and Ni for a coordination sphere of 4 Å using bond valence parameters reported by O'Keeffe (Table S3).…”