Bond angle is 180 degrees. Trigonal-bipyramidal- In this type of molecular geometry, the center atom is surrounded by five atoms. Bond angles are 90 and 120 degrees.

Pop one balloons. Show how the five now conform to trigonal bipyramidal shape. Continue popping balloons one at a time, showing resulting arrangements (4 is tetrahedral, 3 is trigonal planar, 2 is ...

Rotors of this kind may become the components of future miniaturized fluidic devices. The authors based their synthetic design on the trigonal–bipyramidal geometry of an iron complex.