copperammonia

Copperammonia refers to the copper(II) ammine complex formed when copper(II) salts are dissolved in aqueous ammonia. The principal species in moderately concentrated solutions is [Cu(NH3)4(H2O)2]2+, a six‑coordinate complex in which four ammine ligands surround the metal and two water molecules complete the coordination sphere. The solution is typically deep blue.

The complex is a Jahn–Teller distorted octahedral copper(II) species. The four NH3 ligands occupy equatorial positions while two water ligands are axially bound, contributing to the characteristic color and reactivity of the solution. The blue hue arises from ligand‑field transitions in the copper(II) center and is maintained in appropriate ammoniacal conditions; dilution or protonation shifts the equilibrium toward simpler aqua copper species or precipitates copper hydroxide.

Preparation and equilibria: Adding ammonia to a copper(II) salt such as copper sulfate or copper nitrate generates the pale blue solution that rapidly turns deep blue as the ammine complex forms. A simplified representation is Cu2+ + 4 NH3 + 2 H2O ⇌ [Cu(NH3)4(H2O)2]2+. In strongly concentrated ammonia the complex remains stable; increasing water content or lowering pH shifts the equilibrium back, potentially leading to hydrolysis and precipitation.

Applications and notes: The copperammonia complex is a classic reagent in qualitative inorganic analysis for copper detection and in certain qualitative and quantitative procedures. Its vivid blue color provides a convenient visual indicator of copper(II) in solution. The system also serves as a model for studying ligand‑field effects in transition‑metal coordination chemistry.

Safety: Ammonia is caustic and irritant; copper salts can be hazardous if ingested or inhaled. Work in a well‑ventilated area with appropriate protective equipment and follow disposal guidelines.