Nickel tetracarbonyl. A highly toxic, but very useful organonickel compound. Nickel tetracarbonyl is produced industrially during the purification of nickel metal. It is synthesised by passing carbon monoxide gas over impure nickel at 130˚C to selectively remove pure nickel. The gas is then heated up to 250˚C where it will decompose back into nickel metal and carbon monoxide. As with most nickel salts, nickel tetracarbonyl is very toxic, with its LD50 being around 3ppm for a 30 minute exposure.