 The apparent equivalency arises from the low barrier for pseudorotation via the Berry mechanism, by which the axial and equatorial fluorine atoms rapidly exchange positions.Pentacoordinate molecules of trigonal pyramidal geometry typically exhibit a particular kind of low energy fluxional behavior called Berry pseudorotation.Famous examples of such molecules are iron pentacarbonyl (Fe(CO)5) and phosphorus pentafluoride (PF5).