# Coordination number of complex resulting from sodium nitroprusside test

In my textbook the following reaction is given to identify sulfide ion:

$$\ce{Na2[Fe(CN)5(NO)] + Na2S -> \underset{\text{violet solution}}{Na4[Fe(CN)5NOS]}}$$

Here's what I want to know:

Is $$\ce{NOS}$$ a newly formed ligand? If so, what is it called? What is the charge on it? (I'm confused about the charge because of what I've read about NO as a ligand)

If not, then does sulphide act as an independent ligand here? Then does iron show a coordination number of 7 in this complex?