CuII

CuII, shorthand for copper(II), denotes copper in the +2 oxidation state, commonly encountered in inorganic and coordination chemistry. In aqueous solution, copper(II) forms the hexaaqua complex [Cu(H2O)6]2+, which shows Jahn-Teller distortion and a distorted octahedral arrangement rather to an ideal octahedron.

The electronic configuration of CuII is [Ar]3d9, giving one unpaired electron. This makes CuII ions paramagnetic and often responsible for the characteristic blue colors observed in many copper(II) salts and solutions, including copper sulfate. In solid compounds, the color and geometric preferences of CuII arise from ligand field effects and Jahn-Teller distortions, typically producing square planar or elongated octahedral coordination geometries.

In coordination chemistry, CuII forms a wide range of complexes with oxygen, nitrogen, and sulfur donors. Common geometries include distorted octahedral and square planar. Ligands such as water, ammonia, chloride, and organic chelators stabilize diverse structures, from [Cu(H2O)6]2+ to tetracoordinate square-planar species like [CuCl4]2-. Jahn-Teller effects often elongate the axial bonds in octahedral CuII complexes, affecting spectra and reactivity.

Biologically, copper is an essential trace element. CuII participates in redox processes and is found in enzymes such as cytochrome c oxidase and superoxide dismutase, where copper cycles between oxidation states during catalysis. Copper cycling is central to cellular respiration and defense against oxidative stress, but free CuII can catalyze harmful radical formation if mismanaged.

Common CuII compounds include copper sulfate pentahydrate, copper chloride, and basic copper carbonates used as pigments and catalysts. Copper salts can be toxic in excess, requiring careful handling.