Argon (Ar) is a noble gas and is generally unreactive. It doesn't readily form compounds like other elements. However, there are a few rare and unstable compounds where argon is present:

1. Argon Fluorohydride (HArF): This is a very unstable compound formed under high pressure and low temperature. It's the only known neutral compound of argon.

2. Argon Hydride Ion (ArH+): This is a cationic species observed in the interstellar medium and laboratory experiments.

3. Argon Fluoride Ion (ArF-): This is an anionic species observed in laboratory experiments.

4. Argon Complexes: Argon can form weak, transient complexes with other molecules, particularly with highly polar molecules like water. These are not true chemical compounds but rather short-lived interactions.

5. Argon clathrates: Argon can be trapped within the cages of certain crystalline structures called clathrates. These are not chemical compounds but rather physical mixtures.

It's important to note that these compounds are extremely rare and unstable, making them challenging to study and not relevant for everyday applications. Argon is primarily used in its elemental form for various purposes, such as inert atmospheres in welding and manufacturing, and lighting in fluorescent lamps.