1. Mononuclear carbonyl metals

1.1 Metals with even atomic numbers

The action of carbon monoxide on nickel metal leads to nickel carbonyl :

This compound is a volatile, colorless, highly toxic liquid with a boiling point of 34°C. These characteristics were very surprising at the time of its discovery, a time when the idea of covalent bonding as defined by Lewis was not yet advanced. It was soon discovered that this compound is sensitive to heat, and a higher temperature will decompose it: