Direct Reaction between Copper and Nitrogen at High Pressures and Temperatures.

Transition-metal nitrides have applications in a range of technological fields. Recent experiments have shown that new nitrogen-bearing compounds can be accessed through a combination of high temperatures and pressures, revealing a richer chemistry than was previously assumed. Here, we show that at pressures above 50 GPa and temperatures greater than 1500 K  elemental copper reacts with nitrogen, forming copper diazenide (CuN ₂ ). Through a combination of synchrotron X-ray diffraction and first-principles calculations we have explored the stability and electronic structure of CuN ₂ . We find that the novel compound remains stable down to 25 GPa before decomposing to its constituent elements. Electronic structure calculations show that CuN ₂ is metallic and exhibits partially filled N ₂ antibonding orbitals, leading to an ambiguous electronic structure between Cu ⁺ /Cu ²⁺ . This leads to weak Cu-N bonds and the lowest bulk modulus observed for any transition-metal nitride.