metallurgy - Do there exist metals that are composed of molecules?

Most metals are composed of pure elements or are alloys (mixtures of pure elements.)

Are there metals that are composed of one type of molecule that is metallically bonded together?

The difference between a metal that is composed of one type of compound and an alloy is that in an alloy different elements are attached by metallic bonding but in a metal composed of one compound covalent or ionic bonding attaches multiple atoms together into compounds and then these compounds form metallic bonds with each other.

I have read that Gallium in its pure elemental state forms pairs which are then metallically bonded together which sort of is what I'm wondering about except that I'm wondering if metals can form out of more complicated compounds.

I would also expect there to be a lot of compounds which on their own do not form metals but do not degrade the metallicity of alloys they are put in very much.

I think a more specific and low level question might be: are there covalent compounds that can make metallic bonds with other things?

Answer

Sort of, if you define metals as substances that exhibit some metallic behaviour

Metallic elements are, well, the metals. But other substances can exhibit many of the properties of those metals.

One well-known example if what you get when you dissolve a lot of sodium in liquid ammonia. Beyond a certain concentration, a new metallic-like phase if formed where electrons are solvated in the liquid (which contains ammonia molecules). The bronze, metallic colour of this phase is seen in this Periodic Video.

Many metallic properties are dependent on the delocalisation of electrons. Some conjugated polymers can have delocalised electrons and metallic levels of conductivity when doped. Whether these should count as metals is debatable but they do exhibit some metallic properties. And they won a Nobel prize for Heeger, et al. See Wikipedia for some discussion.

So there are molecular systems with some metallic properties, though their bonding is not necessarily because of the electron delocalisation.