High‐Pressure Synthesis of Metal–Inorganic Frameworks Hf(4)N(20)⋅N(2), WN(8)⋅N(2), and Os(5)N(28)⋅3 N(2) with Polymeric Nitrogen Linkers

Polynitrides are intrinsically thermodynamically unstable at ambient conditions and require peculiar synthetic approaches. Now, a one‐step synthesis of metal–inorganic frameworks Hf(4)N(20)⋅N(2), WN(8)⋅N(2), and Os(5)N(28)⋅3 N(2) via direct reactions between elements in a diamond anvil cell at pressures exceeding 100 GPa is reported. The porous frameworks (Hf(4)N(20), WN(8), and Os(5)N(28)) 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 N(2) also leads to a non‐centrosymmetric polynitride Hf(2)N(11) that features double‐helix catena‐poly[tetraz‐1‐ene‐1,4‐diyl] nitrogen chains [−N−N−N=N−](∞).