Sodium hydrosulfide

Structure and properties

Crystalline NaHS undergoes two phase transitions. At temperatures above 360 K, NaSH adopts the NaCl structure, which implies that the HS⁻ behaves as a spherical anion owing to its rapid rotation, leading to equal occupancy of eight equivalent positions. Below 360 K, a rhombohedral structure forms, and the HS⁻ sweeps out a discoidal shape. Below 114 K, the structure becomes monoclinic. The analogous rubidium and potassium compounds behave similarly.

NaSH has a relatively low melting point of 350 °C. In addition to the aforementioned anhydrous forms, it can be obtained as two different hydrates, NaSH·2H₂O and NaSH·3H₂O. These three species are all colorless and behave similarly, but not identically. It can be used to precipitate other metal hydrosulfides, by treatment of aqueous solutions of their salts with sodium hydrosulfide. It is analogous to sodium hydroxide, and is a strong base.