In
chemistry, a pentagonal bipyramid is a
molecular geometry
Molecular geometry is the three-dimensional space, three-dimensional arrangement of the atoms that constitute a molecule. It includes the general shape of the molecule as well as bond lengths, bond angles, torsional angles and any other geometric ...
with one atom at the centre with seven
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 ele ...
s at the corners of a
pentagonal bipyramid
In geometry, the pentagonal bipyramid (or dipyramid) is third of the infinite set of face-transitive bipyramids, and the 13th Johnson solid (). Each bipyramid is the dual of a uniform prism.
Although it is face-transitive, it is not a Platoni ...
. A perfect pentagonal bipyramid belongs to the
molecular point group ''D
5h''.
The pentagonal bipyramid is a case where bond angles surrounding an atom are not identical (see also
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 ident ...
). This is one of the three common shapes for heptacoordinate transition metal complexes, along with the
capped octahedron and the
capped trigonal prism.
Pentagonal bipyramids are claimed to be promising coordination geometries for
lanthanide
The lanthanide () or lanthanoid () series of chemical elements comprises the 15 metallic chemical elements with atomic numbers 57–71, from lanthanum through lutetium. These elements, along with the chemically similar elements scandium and y ...
-based
Single-molecule magnets
A single-molecule magnet (SMM) is a metal-organic compound that has superparamagnetic behavior below a certain blocking temperature at the molecular scale. In this temperature range, a SMM exhibits magnetic hysteresis of purely molecular origin.< ...
, since (a) they present no
extradiagonal Crystal Field Crystal field theory (CFT) describes the breaking of degeneracies of electron orbital states, usually ''d'' or ''f'' orbitals, due to a static electric field produced by a surrounding charge distribution (anion neighbors). This theory has been used ...
terms, therefore minimising spin mixing, and (b) all of their diagonal terms are in first approximation protected from low-energy vibrations, minimising
vibronic coupling
Vibronic coupling (also called nonadiabatic coupling or derivative coupling) in a molecule involves the interaction between electronic and nuclear vibrational motion. The term "vibronic" originates from the combination of the terms "vibrational" a ...
.
Examples
*
Iodine heptafluoride
Iodine heptafluoride, also known as iodine(VII) fluoride or iodine fluoride, is an interhalogen compound with the chemical formula I F7. It has an unusual pentagonal bipyramidal structure, as predicted by VSEPR theory. The molecule can undergo ...
(IF
7) with 7 bonding groups
*
Peroxo chromium
Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal.
Chromium metal is valued for its high corrosion resistance and h ...
(IV) complexes, e.g.
r(O2)2(NH3)3where the peroxo groups occupy four of the planar positions.
* and
References
External links
– Images of IF
7
3D Chem– Chemistry, Structures, and 3D Molecules
IUMSC– Indiana University Molecular Structure Center
{{MolecularGeometry
Stereochemistry
Molecular geometry