chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a physical science within the natural sciences that studies the chemical elements that make up matter and chemical compound, compounds made of atoms, molecules a ...

, the capped square antiprismatic molecular geometry describes the shape of compounds where nine atoms, groups of atoms, or

ligand In coordination chemistry, a ligand is an ion or molecule with a functional group that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's el ...

s are arranged around a central atom, defining the vertices of a gyroelongated square pyramid. The

symmetry group In group theory, the symmetry group of a geometric object is the group of all transformations under which the object is invariant, endowed with the group operation of composition. Such a transformation is an invertible mapping of the amb ...

of the resulting object is C_4v. The gyroelongated square pyramid is a

square pyramid In geometry, a square pyramid is a Pyramid (geometry), pyramid with a square base and four triangles, having a total of five faces. If the Apex (geometry), apex of the pyramid is directly above the center of the square, it is a ''right square p ...

with a

square antiprism In geometry, the square antiprism is the second in an infinite family of antiprisms formed by an even number, even-numbered sequence of triangle sides closed by two polygon caps. It is also known as an ''anticube''. If all its faces are regular ...

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 In chemistry, the tricapped trigonal prismatic 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 triaugmented triangular prism (a trigon ...

, and there is some dispute over the specific geometry exhibited by certain molecules. Examples: * iCo₉(CO)₂₁sup>2-, defined by the Co₉ framework, which encapsulates the Si atom * b(phen)₄(OClO₃)sup>+, defined by the N₈O framework, which encapsulates the Pb²⁺ ion * e₉sup>4−, a zintl ion *Th( troopolonate)₄(H₂O), defined by the O₉ framework, which encapsulates the Th⁴⁺ ion * is sometimes described as having a capped square antiprismatic geometry, although its geometry is most often described as tricapped trigonal prismatic. *, a

lanthanum Lanthanum is a chemical element; it has symbol La and atomic number 57. It is a soft, ductile, silvery-white metal that tarnishes slowly when exposed to air. It is the eponym of the lanthanide series, a group of 15 similar elements bet ...

(III) 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 In geometry, the gyroelongated square bipyramid is a polyhedron with 16 triangular faces. it can be constructed from a square antiprism by attaching two equilateral square pyramid, equilateral square pyramids to each of its square faces. The same ...

. The

of this object is D_4d. Examples: *B₁₀H₁₂, defined by the B₁₀ framework * sRh₁₀(CO)₂₂sup>3− and Rh₁₀(CO)₂₂sup>2−, defined by the Rh₁₀ framework, which encapsulates the main group atoms As and S * lSn₈sup>3−, a zintl ion

References

Stereochemistry Molecular geometry {{molecular-geometry-stub