Well, the fact that sulfuric acid (as opposed to sulfuric (VI) acid) has been accepted for your last compound would lead me to try strontium nitride.
Sulfuric (IV) acid exists as well, though I've never seen it named as such - sulfurous acid H2SO3. I have seen nitrous (HNO2) referred to as nitric (III), and nitric (HNO3) as nitric (V) acids. which is the basis of my assertion here.
Do any of your peers have Sr3N2 in their selection, have they named it correctly?