Question

Explain the structure of [Cu(NH₃)₂]²⁺ on the basis of valence bond theory.

Answer 1

1. The complex [Cu(NH₃)₂]²⁺ contains copper (Cu) and ammonia (NH₃) ligands.
2. Since ammonia is a neutral ligand, the overall charge of the complex [Cu(NH₃)₂]²⁺ suggests that copper is in the +2 oxidation state with an electronic configuration of [Ar] 3d⁹.
3. In the complex [Cu(NH₃)₂]²⁺, the coordination number of copper is 2, because there are two ammonia ligands coordinating with the central copper ion.
4. A coordination number of 2 typically leads to a linear geometry.
5. To form the bonds with the two ammonia molecules, copper undergoes sp hybridisation. This involves the mixing of one s-orbital and one p-orbital from the copper ion to form two hybrid orbitals.
6. These two hybrid orbitals are aligned in a linear arrangement, resulting in a linear geometry for the complex.
7. Since Cu²⁺ has 9 electrons in its 3d orbitals and one of these is unpaired, the complex contains one unpaired electron.

Therefore, the complex is paramagnetic, because there is at least one unpaired electron.