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

Solution 1:

According to A Conducting Crystal Based on A Single-Component Paramagnetic Molecule, [Cu(dmdt)2] (dmdt ) Dimethyltetrathiafulvalenedithiolate) J. Am. Chem. Soc., 2002, 124 (34), pp 10002–10003 :

Single-component molecular metals should greatly extend the development of new types of molecular conductors. For example, while the first metallic molecule-based magnet has been reported recently, [reference 8] it may be possible to create such metallic molecular magnets from single-component molecules containing paramagnetic ions such as Cu2+ and Co2+.

Reference 8 is Coexistence of ferromagnetism and metallic conductivity in a molecule-based layered compound Nature 408, 447-449

The temperature dependence of the resistance exhibits a metallic behaviour over the entire temperature range that we investigated (down to 2 K).

Solution 2:

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.

---

Solution 3:

Yes mercury can form an amalgam with ammonium that is $\ce{H3N-Hg-H}$ although it decomposes at room temperature.

See https://en.wikipedia.org/wiki/Amalgam_%28chemistry%29#Ammonium_amalgam

It might be possible to do this with more chemicals and mercury.

Theoretically cations like Ammonium might have a metallic nature but I wouldn't know the details of that.

---

Solution 4:

Yes

Adding to the other examples, there is an elemental diatomic metal.

No that's not a typo.

I'm sure you learned your diatomics in school: H₂, N₂, O₂, F₂, Cl₂, Br₂, and I₂. They probably gave you the rather awkward acronym "HOFBrINCl" as well. In college you may have learned that at high enough temperatures S₂ and possibly even P₂ can exist in equilibrium with other species.

But at STP there's still one missing from that list, right between Cl₂ and Br₂. That missing diatomic is gallium metal. In fact, the covalent Ga₂ pairs are why gallium melts at such a low temperature.