Here's an unusual twist: a single element compound. Think about it. I'm not talking about an allotrope such as all the various forms carbon can take: diamond, graphite, buckyballs... Those "compounds" are made of nothing but covalent bonds and all the bonds are the same. This new compound is an element that is able to ionically bond to itself, a feat that would normally requires a difference in electronegativity between the atoms, and is normally considered an impossibility because there is just one element here. The article I linked to above is in Nature (one way or the other, it's going to cost you) while this article is a good review of not only this work, but also the history of boron research.
To paraphrase George Orwell, "All boron atoms are equal; but some boron atoms are more equal than others."