High‐pressure synthesis of metal‐inorganic frameworks Hf4N20·N2, WN8·N2, and Os5N28·3N2 with polymeric nitrogen linkers

The synthesis of various polynitrogen compounds have been actively pursued for the past hundred years due to their potential as high energy density materials. Polynitrides are intrinsically thermodynamically unstable at ambient conditions and require peculiar synthetic approaches. Here we report one-step synthesis of metal-inorganic frameworks Hf 4 N 20 .N 2 , WN 8 .N 2 , and Os 5 N 28 .3N 2 via direct reactions between elements in a diamond anvil cell at pressures exceeding 100 GPa. 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. Due 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-] infinity .