1. 16-electron environment

In the light of Delépine's work on iridium chemistry, the following iridium(I) compound can be prepared by redox, with ethanol as the reducing agent and iridium(III) as the oxidizing agent:

Carbon monoxide comes from the ethanol used as a solvent. This complex is square planar. It corresponds to an iridium atom surrounded by 16 electrons. A radical count that ignores oxidation states gives :

iridium: 9 electrons chlorine: 1 electron

phosphine: 2 × 2 electrons carbon monoxide: 2 electrons

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