copperII

Copper(II) refers to the oxidation state +2 of copper, symbolized as Cu2+. In aqueous solution, copper(II) is typically present as the hexaaquacopper(II) ion, [Cu(H2O)6]2+, which is blue. The ion is paramagnetic (one unpaired electron) and exhibits Jahn–Teller distortions in octahedral coordination, leading to elongated axial bonds in many complexes.

Common copper(II) compounds include copper(II) sulfate pentahydrate (CuSO4·5H2O), which is bright blue; copper(II) chloride (CuCl2), which is brown-green in the solid and blue in solution; copper(II) oxide (CuO), a black solid; and copper(II) hydroxide, Cu(OH)2, a pale blue solid that converts to CuO on heating. Minerals containing copper(II) include tenorite (CuO), malachite Cu2(CO3)(OH)2, and azurite Cu3(CO3)2(OH)2.

In coordination chemistry and biology, copper(II) forms numerous complexes with ligands such as water, ammonia, and halides. Copper is an essential trace element in many enzymes and transport proteins; its redox couple Cu2+/Cu+ participates in electron transfer reactions.

In organic synthesis and catalysis, copper(II) salts can serve as precatalysts; they are reduced in situ to copper(I), which catalyzes reactions such as the azide–alkyne cycloaddition and various oxidation processes.

Safety: soluble copper(II) salts are toxic in sufficient quantities and can cause irritation. Waste disposal should follow chemical waste guidelines.