Pentagonal bipyramidal molecular geometry

In chemistry, a pentagonal bipyramid is a molecular geometry with one atom at the centre with seven ligands at the corners of a pentagonal bipyramid. A perfect pentagonal bipyramid belongs to the molecular point group D_5h.

Pentagonal bipyramidal molecular geometry
Examples	IF7, ZrF3−7
Point group	D5h
Coordination number	7
Bond angle(s)	90°, 72°
μ (Polarity)	0

Structure of iodine heptafluoride, an example of a molecule with the pentagonal-bipyramidal coordination geometry.

The pentagonal bipyramid is a case where bond angles surrounding an atom are not identical (see also trigonal bipyramidal molecular geometry).^{[1][page needed]} This is one of the three common shapes for heptacoordinate transition metal complexes, along with the capped octahedron and the capped trigonal prism.^{[2][3][page needed]}

Pentagonal bipyramids are claimed to be promising coordination geometries for lanthanide-based single-molecule magnets, since they present no extradiagonal crystal field terms, therefore minimising spin mixing, and all of their diagonal terms are in first approximation protected from low-energy vibrations, minimising vibronic coupling.^[4]

Examples

• Iodine heptafluoride (IF₇) with 7 bonding groups
• Rhenium heptafluoride (ReF₇)
• Peroxo chromium(IV) complexes, e.g. [Cr(O₂)₂(NH₃)₃] where the peroxo groups occupy four of the planar positions.
• ZrF³⁻
  ₇ and HfF³⁻
  ₇^[5][6]