Station Nigala IV was a space station.

In 2366, it was the destination of the USS Enterprise-D following its humanitarian mission to Bre'el IV. (TNG: "Deja Q")

This space station was only mentioned in dialogue.
According to Star Trek: Star Charts ("United Federation of Planets III") and Stellar Cartography: The Starfleet Reference Library ("Federation Historical Highlights, 2161-2385"), Station Nigala IV was located in the Alpha Quadrant.