# What do dashes mean in chemical formulas?

I'm working on summarizing some research for an essay; here's the main article.

The basic premise is making nanoparticles from gold and iron(III) oxide that have properties of both gold and iron.

The formula they give is $\ce{Fe2O3-Au}$. The procedure involves chemical reactions, so I'm assuming it is a new molecule or particle of some sort, but what does the dash mean in the formula? Does it relate to the type of bond or something?

Also, and this is probably bonus since the useful part of the question deals with dash notation, but from the procedure I've generated the partial equation:

$$\ce{Fe2O3 + H2O + Na3C6H5O7 + HAuCl4 → Fe2O3-Au} + \text{something}...$$

After the reaction, the samples are put through a centrifuge and some unknown supernate is then removed, leaving the $\ce{Fe2O3-Au}$. Do you have any guesses on what the supernate is composed of? I was thinking something along the lines of $\ce{HCl}$, but I'm not sure what would happen to the sodium or carbon.

This nomenclature refers to a core-shell arrangement of nanoparticles. This is where you have a nanoparticle core consisting of one material that has been coated/decorated/wrapped/overlaid with another material. There are a few accepted forms of nomenclature for describing these types of nanoparticles:

• core@shell In your case, it would be Fe2O3@Au
• core-shell In your case, it would be Fe2O3-Au
• core/shell In your case, it would be Fe2O3/Au

There are plenty of examples of each syntax in the literature, and has been used for eons.