Nitro-cobalt, Co₂(NO₂)

Nitro-cobalt, Co₂(NO₂), is obtained as a black mass when nitrogen peroxide suitably diluted with nitrogen is passed over reduced cobalt. Water decomposes it vigorously, cobalt nitrate with very little nitrite is produced, together sometimes with a basic salt. When heated in nitrogen it evolves nitrous fumes, then decomposes with almost explosive violence, leaving a mixture of cobalt and its oxide.