nickel tetracarbonyl

Other names: tetracarbonylnickel, Mond nickel

[Ni(CO)₄]

37/50 uncommon

Nickel tetracarbonyl is a heavy, volatile liquid central to the Mond process – an industrial method developed in 1890 to purify nickel. This elegant process relies on a remarkable chemical property: at about 50°C, carbon monoxide combines with impure nickel to form Ni(CO)₄, which then decomposes back to pure nickel when heated to 230°C. The industrial significance of this compound is matched only by its extraordinary toxicity. As Derek Lowe aptly describes in his "Things I Won't Work With" series, this flammable liquid can spontaneously ignite in air and possesses an LD₅₀ of merely 3 ppm. Exposure is doubly lethal: the carbon monoxide ligands attack hemoglobin, while free nickel ions literally plate metallic nickel onto lung tissue. Despite having a vapor pressure near that of water – meaning it readily becomes an inhalable gas – there exist reports of its "characteristic" musty odor[1]. That anyone has survived to describe this smell seems miraculous given that a single breath can be fatal. Despite these terrifying properties, the Mond process remains in use today, though with extensive engineering controls that prevent human exposure to this necessary but nightmarish industrial intermediate.

[1] it always makes me chuckle when qualitative features of reagents (smell, color, etc) are described as 'characteristic'. just like "you'll know it when you see it bro" lmao ↩