In chemistry, T-shaped molecular geometry describes the structures of some molecules where a central atom has three

ligand In coordination chemistry, a ligand is an ion or molecule (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 electr ...

s. Ordinarily, three-coordinated compounds adopt

trigonal planar In chemistry, trigonal planar is a molecular geometry model with one atom at the center and three atoms at the corners of an equilateral triangle, called peripheral atoms, all in one plane. In an ideal trigonal planar species, all three ligands a ...

pyramidal A pyramid (from el, πυραμίς ') is a structure whose outer surfaces are triangular and converge to a single step at the top, making the shape roughly a pyramid in the geometric sense. The base of a pyramid can be trilateral, quadrilater ...

geometries. Examples of T-shaped molecules are the halogen trifluorides, such as ClF₃. According to

VSEPR theory Valence shell electron pair repulsion (VSEPR) theory ( , ), is a model used in chemistry to predict the geometry of individual molecules from the number of electron pairs surrounding their central atoms. It is also named the Gillespie-Nyholm theo ...

, T-shaped geometry results when three ligands and two lone pairs of electrons are bonded to the central atom, written in AXE notation as AX₃E₂. The T-shaped geometry is related to the

trigonal bipyramidal molecular geometry In chemistry, a trigonal bipyramid formation is a molecular geometry with one atom at the center and 5 more atoms at the corners of a triangular bipyramid. This is one geometry for which the bond angles surrounding the central atom are not identi ...

for AX₅ molecules with three equatorial and two axial ligands. In an AX₃E₂ molecule, the two lone pairs occupy two equatorial positions, and the three ligand atoms occupy the two axial positions as well as one equatorial position. The three atoms bond at 90° angles on one side of the central atom, producing the T shape. The trifluoroxenate(II) anion, , has been investigated as a possible first example of an AX₃E₃ molecule, which might be expected by VSEPR reasoning to have six electron pairs in an

octahedral In geometry, an octahedron (plural: octahedra, octahedrons) is a polyhedron with eight faces. The term is most commonly used to refer to the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet at ea ...

arrangement with both the three lone pairs and the three ligands in a ''mer'' or T-shaped orientations. Although this anion has been detected in the gas phase, attempts at synthesis in solution and experimental structure determination were unsuccessful. A

computational chemistry Computational chemistry is a branch of chemistry that uses computer simulation to assist in solving chemical problems. It uses methods of theoretical chemistry, incorporated into computer programs, to calculate the structures and properties of m ...

study showed a distorted planar Y-shaped geometry with the smallest F–Xe–F bond angle equal to 69°, rather than 90° as in a T-shaped geometry.

References

External links

Chem, Chemistry, Structures, and 3D Molecules

Indiana University Molecular Structure Center

{{MolecularGeometry Molecular geometry

See also

References

External links