How can nitrogen be quadruply bonded in tris(8-hydroxyquinoloinato)aluminum?

Nitrogen typically has five outer valence electrons. So how does a triply-bonded nitrogen in 8-hydroxyquinoline end up quadruply bonded in [tris(8-hydroxyquinolinato)aluminum](https://en.wikipedia.org/wiki/Tris(8-hydroxyquinolinato)aluminium)? 


