Which configuration is typically adopted by a central ion with a d8 electron configuration when all ligands are identical?

A central ion with a d8 electron configuration often adopts a square planar geometry when all ligands are identical. This preference can be attributed to the electronic and steric factors that influence the arrangement of ligands around the metal center.

In the case of d8 metal ions, such as Ni(II) and Pt(II), the square planar configuration allows for effective overlap of the metal's d orbitals with those of the ligands, leading to strong bonding interactions. This arrangement stabilizes the complex due to minimal electronic repulsion among the ligands, which are positioned at 90-degree angles to each other.

Moreover, the square planar geometry also helps in accommodating the specific spatial requirements of d8 configurations, where the presence of paired electrons in the metal's orbitals can lead to less steric hindrance compared to other geometries. This is particularly relevant when considering ligand size and the potential for steric clashes in arrangements like octahedral or tetrahedral.

In summary, the square planar configuration is favored for d8 metal complexes with identical ligands due to its balance of electrostatic and steric factors, resulting in enhanced stability and effective orbital overlap.