2NiOH2

2NiOH2 is the notation for two units of nickel(II) hydroxide, Ni(OH)2. Nickel(II) hydroxide is an inorganic compound that appears as a pale green solid and is sparingly soluble in water. In the solid, it adopts a layered brucite-like structure with octahedrally coordinated Ni2+ centers linked by hydroxide ligands.

Preparation and structure: Ni(OH)2 is typically prepared by precipitation from nickel(II) salts with hydroxide bases, such as adding NaOH to an aqueous Ni2+ solution to form a green Ni(OH)2 precipitate, which is then filtered and dried. The solid can be heated to higher temperatures to yield nickel oxide, NiO.

Chemical properties: Ni(OH)2 is a basic solid that dissolves in acids to give Ni2+ salts and water: Ni(OH)2 + 2 H+ → Ni2+ + 2 H2O. In strongly basic solutions it can form soluble nickelate or complex species under certain conditions, reflecting limited amphoteric behavior. It is relatively stable under ambient conditions but oxidizes or dehydrates upon heating, ultimately converting to NiO.

Applications and role: Ni(OH)2 is an important precursor to nickel oxide (NiO) and nickel oxyhydroxide (NiOOH), which are used in various catalytic and electrochemical applications. In rechargeable nickel-based batteries, Ni(OH)2 participates in redox processes associated with the electrode materials, alternating with NiOOH during charge and discharge cycles.

Safety: Nickel compounds, including Ni(OH)2, are considered potentially hazardous and should be handled with appropriate safety precautions to avoid inhalation or dermal exposure.

Note: 2NiOH2 is not a distinct chemical species beyond a stoichiometric representation; it simply indicates two equivalents of Ni(OH)2 in a formulation or reaction.