High‐Pressure Synthesis of Metal–Inorganic Frameworks Hf₄N₂₀⋅N₂, WN₈⋅N₂, and Os₅N₂₈⋅3 N₂ with Polymeric Nitrogen Linkers

Abstract

Polynitrides are intrinsically thermodynamically unstable at ambient conditions and require peculiar synthetic approaches. Now, a one‐step synthesis of metal–inorganic frameworks Hf4N20⋅N2, WN8⋅N2, and Os5N28⋅3 N2 via direct reactions between elements in a diamond anvil cell at pressures exceeding 100 GPa is reported. The porous frameworks (Hf4N20, WN8, and Os5N28) are built from transition‐metal atoms linked either by polymeric polydiazenediyl (polyacetylene‐like) nitrogen chains or through dinitrogen units. Triply bound dinitrogen molecules occupy channels of these frameworks. Owing to conjugated polydiazenediyl chains, these compounds exhibit metallic properties. The high‐pressure reaction between Hf and N2 also leads to a non‐centrosymmetric polynitride Hf2N11 that features double‐helix catena‐poly[tetraz‐1‐ene‐1,4‐diyl] nitrogen chains [−N−N−N=N−]∞.

One-Dimensional Non-coplanar Nitrogen Chains in Manganese Tetranitride under High Pressure

“…The asymmetric interactions drive the N 1 and N 4 atoms to hybridize between sp 2 and sp 3 (the green one in Figure c,d) and lead to the distortions of [N 4 ] chains (Figure d). Previous studies of TaN 5 and FeN 4 have also proved that the [N n ] chains hybridized with sp 3 have distortion, while all sp 2 hybridization [N n ] chains (ZnN 4 and WN 8 ·N 2 ) have no distortion. The distorted [N n ] chains are first observed in the MnN 4 .…”

“…The mass energy density (2.97 kJ/g) and volume energy density (13.84 kJ/cm 3 ) of MnN 4 = MnN + 3/2N 2 40 are also larger than most polynitrides characterized by [N 4 ] chains. 30,32,46,47 So, P-1 MnN 4 could be considered as a HEDM, and this structure possesses distortion [N 4 ] chains and will lay a foundation for the design of HEDM in the future.…”

“…Previous work has suggested that the introduction of metal elements will be an electron donor to stabilize the polymeric unit in polynitrides . Because of the various valence electrons, transition metals (TM) as better electron donors had been extensively reported in first-principles calculations of polynitrides. − Theoretical calculations predicted the existence of different polynitrides MN x (M = transition metal, x = 4–10) featuring various polymeric nitrogen networks such as 1D infinity zigzag chains (ZnN 4 , , FeN 4 , , and WN 8 ·N 2 ), triangular structures (IrN 4 ), N 5 rings (IrN 7 , ScN 6 , ZnN 10 ), armchair-like N 6 rings (WN 6 , , MoN 6 , ReN 6 ), a 3D network (ScN 7 ), branched chains (TaN 5 ), and N 18 macrocycles (YN 6 ). On the one hand, these nitrides have a variety of properties because of the different nitrogen configurations.…”

“…Comparing the average bond lengths (1.32 Å at 108 GP and 1.34 Å at 56 GPa) between adjacent nitrogen atoms in MnN 4 with other experimentally reported polynitrides in Table , it can be seen that the average bond length of the [N 4 ] unit in MnN 4 is larger than many synthesized polynitrides. The mass energy density (2.97 kJ/g) and volume energy density (13.84 kJ/cm 3 ) of MnN 4 = MnN + 3/2N 2 are also larger than most polynitrides characterized by [N 4 ] chains. ,,, So, P -1 MnN 4 could be considered as a HEDM, and this structure possesses distortion [N 4 ] chains and will lay a foundation for the design of HEDM in the future.…”

High‐pressure Synthesis of Cobalt Polynitrides: Unveiling Intriguing Crystal Structures and Nitridation Behavior

“…[1][2][3][4][5][6][7] Transition metal pernitrides (e. g. PtN 2 , ReN 2 , OsN 2 ) containing NÀ N dimers are recognized for their high bulk modulus and potential applications as superhard materials. [1,8,9] Polynitrides containing polymeric nitrogen chains (such as FeN 4, [2] TaN 5, [10] MgN 4, [11] WN 10, [12] YN 6 [13] ) represent higher levels of nitridation. More recently, experimental studies have uncovered nitrogen rings including pentazolates (N 5 À ), hexazine anions N 6 xÀ and N 18 .…”