Capped square antiprismatic molecular geometry

Point group	C_4v
Coordination number	9

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 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 (a square antiprism with a pyramid erected on one of the square faces).

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

ReH²⁻
₉ is sometimes described as having a capped square antiprismatic geometry, although its geometry is most often described as tricapped trigonal prismatic.
[LaCl(H
₂O)
₇]⁴⁺
₂, a lanthanum(III) complex with a La–La bond.^[1]

References

^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 917. ISBN 978-0-08-037941-8.

v t e Molecular geometry
VSEPR theory Coordination number
Coordination number 2	Linear Bent
Coordination number 3	Trigonal planar Trigonal pyramidal T-shaped
Coordination number 4	Tetrahedral Square planar Seesaw
Coordination number 5	Trigonal bipyramidal Square pyramidal Pentagonal planar
Coordination number 6	Octahedral Trigonal prismatic Pentagonal pyramidal
Coordination number 7	Pentagonal bipyramidal Capped octahedral Capped trigonal prismatic
Coordination number 8	Square antiprismatic Dodecahedral Bicapped trigonal prismatic
Coordination number 9	Tricapped trigonal prismatic Capped square antiprismatic
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