The term carbonyl can also refer to carbon monoxide as a ligand in an inorganic or organometallic complex (a metal carbonyl, e.g. nickel carbonyl). A carbonyl group characterizes the following types of compounds.

By itself or part of an alloy consisting of other metals. It can be also used as a compound -

nickel (III) oxide - typically used in one specific type of rechargeable batteries (nickel-cadmium; NiCd)

Mond's process is a the process of extracting and purifying nickel. It was devised by Ludwid Mond in 1899. In this process, nickel is obtained from nickel oxide through a series of steps. This process makes use of the fact that nickel easily combines reversibly with carbon monoxide to give nickel carbonyl.

Carbonyl