Nitro-nickel, Ni₂NO₂

When nitrogen peroxide, suitably diluted with nitrogen, is passed over reduced nickel, a black mass of Nitro-nickel, Ni₂NO₂ is obtained. Water decomposes it vigorously. When heated in a current of nitrogen nitrous fumes are first evolved, then the substance decomposes with violence, leaving a residue of nickel and its oxide.