For which type of atoms or ions is it common to observe high coordination numbers?

High coordination numbers are often observed for f block elements, particularly among the lanthanides and actinides. This is primarily due to the larger ionic radii of these elements and their ability to accommodate more ligands in their coordination sphere. For example, lanthanides can often exhibit coordination numbers of 8, 9, or even higher due to favorable geometries and sufficient space around the metal center.

While d block elements can also exhibit various coordination numbers, they tend to have a more variable range depending on factors such as oxidation state and ligand types. S block elements generally form simpler geometries and coordination environments, often with lower coordination numbers than those seen in f block elements.

Thus, the typical observation of high coordination numbers aligns closely with the properties of the f block elements, explaining why this choice stands out.