[arethuza]

I don't know about that compound being toxic, but there are some splendidly awful fluorine compounds:

http://pipeline.corante.com/archives/2010/02/23/things_i_won...

[Gravityloss]

Though that's completely different, it's an oxidizer.

You have fluorine in your tooth paste. Hell, oxygen can be dangerous, nitrogen is used in a lot of explosives etc etc.