# Oxidation states of boron

I have just been looking at https://en.wikipedia.org/wiki/List_of_oxidation_states_of_the_elements and found that boron has a -5 oxidation state. I would like to know which boron compounds form this oxidation state.

As I remember I have read somewhere that $$\ce{Al3BC}$$ is konwn to have Boron in -5 oxidation state.

• You are correct because (3*3)-5-4=0 Jan 27 '19 at 7:47

It isn't just boron. The same Wikipedia list gives a -5 oxidation state for all the Group 13 elements except nihonium (which is only very recently known) and, more curiously, aluminum. For thallium Wikipedia's article on the element gives this reference, where a compound has thallium in various clusters and individual atoms bonded to alkali metals. The individual atoms at least formally have five negative charges.

• Except for Al, seemingly. Jan 27 '19 at 7:49
• Said that, read again. Jan 27 '19 at 9:30