What type of coordination geometry is less common for five-coordinate complexes?

Five-coordinate complexes can adopt various geometries, but some are more commonly encountered than others. The square pyramidal and trigonal bipyramidal geometries are indeed possible for five-coordinate complexes. However, they are less commonly observed compared to the other geometries available for five-coordinate complexes.

In the case of square planar geometry, it is particularly common in transition metal complexes, especially those with d8 electronic configurations, which are more stable in such arrangements. Tetrahedral geometry, while it typically applies to four-coordinate complexes, can also occasionally occur for five-coordinate complexes but is somewhat less common than other geometries.

Stereoisometric geometry does not describe a specific coordination geometry type but rather refers to the arrangement of ligands around the central metal ion in a way that maintains spatial distinction. This means it doesn't directly represent a concrete structure like the others.

Thus, the combination of square pyramidal or trigonal bipyramidal geometries stands out as less frequently encountered in five-coordinate complexes, making that choice the correct answer for identifying the less common geometry in this context.