- Nickel ammonium sulfate, also known as ammonium nickel(II) sulfate or by its mineral form name Morenosite (when hydrated), is a double salt composed of nickel(II) sulfate (NiSO4) and ammonium sulfate ((NH4)2SO4).
- It typically crystallizes with six water molecules as nickel ammonium sulfate hexahydrate (Ni(NH4)2(SO4)2⋅6H2O), forming green or bluish-green crystals that are soluble in water but insoluble in alcohol. The compound belongs to the class of double sulfates, structurally related to the Tutton salt family, in which a divalent metal ion and a monovalent cation (in this case, ammonium) are both coordinated with sulfate and water molecules in a stable crystalline lattice.
- In its crystalline form, nickel ammonium sulfate exhibits a monoclinic structure, with the nickel ion typically octahedrally coordinated by oxygen atoms from water molecules and sulfate anions. The presence of ammonium ions balances the charge and contributes to the stability of the crystal lattice through hydrogen bonding interactions. The compound’s characteristic green coloration arises from d–d electronic transitions in the Ni²⁺ ion, influenced by the surrounding ligand field formed by the oxygen donors of water and sulfate.
- Nickel ammonium sulfate is commonly synthesized by dissolving stoichiometric amounts of nickel(II) sulfate and ammonium sulfate in water, followed by slow evaporation to induce crystallization. The resulting hexahydrate crystals can be purified by recrystallization. This compound is stable under normal conditions but decomposes upon strong heating, losing water and releasing ammonia and sulfur oxides before finally forming nickel oxide (NiO) as a residue.
- This salt has a number of practical applications. One of its primary uses is in electroplating, where it serves as a source of nickel ions in electroplating baths. Its relatively high solubility and stable nickel content make it a convenient and consistent nickel source. Nickel ammonium sulfate is also used in analytical chemistry, especially in gravimetric and volumetric determinations involving nickel. In addition, it may be used in laboratory demonstrations, crystal growing experiments, and occasionally in catalysis research due to the defined coordination environment around nickel.
- As with all nickel compounds, nickel ammonium sulfate must be handled with caution due to health hazards associated with nickel ions. These include skin sensitization, allergic dermatitis, and respiratory issues upon prolonged or repeated exposure. The compound is considered a potential carcinogen, particularly in occupational settings involving inhalation of fine dust or aerosols. Proper safety procedures, including the use of gloves, eye protection, and fume hoods, are essential when handling this material.
