TetraamminecopperII

Tetraamminecopper(II) is the coordination complex of copper(II) with four ammine (NH3) ligands, commonly represented as [Cu(NH3)4]2+. It is a well-known example in inorganic chemistry and appears in discussions of copper(II) coordination chemistry and qualitative analysis. In aqueous solution, copper(II) ions are typically present as [Cu(H2O)6]2+. When ammonia is added, water ligands are displaced by NH3 to form various mixed-ligand species, and with sufficient ammonia, the tetraammine complex becomes the dominant species, producing a characteristic blue solution. The complex is paramagnetic, reflecting one unpaired electron on copper(II).

Structure and properties: The complex is described as four-coordinate copper(II). In solid salts, the ion pairs and counterions give crystalline materials that reflect the same four-coordinate copper center. In solution the coordination environment around copper is often discussed in terms of a square-planar arrangement, though Jahn–Teller effects and potential association with additional ligands can lead to distortions or alternative coordination geometries in related species. The intense blue color arises from d-d electronic transitions typical of copper(II) complexes.

Relevance and applications: Tetraamminecopper(II) serves as a standard example in teaching coordination chemistry and ligand substitution, illustrating how a strong-field ligand like ammonia can substitute water ligands around copper(II). It also features in qualitative tests and discussions of copper-ammonia equilibria, including the formation of blue solutions upon ammonia addition to copper(II) salts.