Capped square antiprismatic molecular geometry
In chemistry, the capped square antiprismatic molecular geometry describes the shape of compounds where nine atoms, groups of atoms, or ligands are arranged around a central atom, defining the vertices of a gyroelongated square pyramid. The symmetry group of the resulting object is C4v.
The gyroelongated square pyramid is a square pyramid with a square antiprism connected to the square base. In this respect, it can be seen as a "capped" square antiprism.
It is very similar to the tricapped trigonal prismatic molecular geometry, and there is some dispute over the specific geometry exhibited by certain molecules.
Examples:
- 2-, defined by the Co9 framework, which encapsulates the Si atom
- +, defined by the N8O framework, which encapsulates the Pb2+ ion
- 4−, a zintl ion
- Th4, defined by the O9 framework, which encapsulates the Th4+ ion
- [Potassium nonahydridorhenate|] is sometimes described as having a capped square antiprismatic geometry, although its geometry is most often described as tricapped trigonal prismatic.
- , a lanthanum complex with a La–La bond.
Bicapped square antiprismatic molecular geometry
Square antiprisms can be capped on both square faces, giving bicapped square antiprismatic molecular geometry. The bicapped square antiprismatic atoms surrounding a central atom define the vertices of a gyroelongated square bipyramid. The symmetry group of this object is D4d.Examples: