The Pentagonal Bipyramid as Fundamental Structure for Compounds with the Coordination Number Seven

A capped octahedron, a capped trigonal prism, and a pentagonal bipyramid are the three structural types possible for compounds with coordination number 7. TeF, CH3OTeF, and trans-(CH3O)2TeF are all pentagonal bipyramidal; the large methoxy groups take up axial positions. The equatorial F atoms deviate slightly from an ideal plane. The picture on the right shows the crystal structure of TeF, which contains fourfold disordered equatorial fluorine atoms.