Ammonium sulfide

Ammonium sulfide, also known as diammonium sulfide, is a hypothetical salt with the formula [NH4]2S. Aqueous solutions purporting to contain this salt are commercially available. With a pKa exceeding 15, the hydrosulfide ion cannot be deprotonated by ammonia. Thus such solutions consist of a mixture of ammonia and [NH4]SH.

Safety
Solutions of "ammonium sulfide" are hazardous as labile sources of toxic hydrogen sulfide.