Apicophilicity

Apicophilicity is the phenomenon in which electronegative substituents of trigonal bipyramidal pentacoordinate compounds prefer to occupy apical (axial) positions (L_ap).^[1]

The term "apicophilicity" was first proposed by

The apicophilicity of a substituent mainly depends on its electronegativity, but some other factors can also have an effect. A bulky substituent prefers equatorial positions, which are more distant from other substituents. A substituent with π-bonding ability also prefers equatorial positions. The use of multidentate ligands can also control the arrangement of substituents. For example, a bidentate ligand with a five-membered ring structure greatly stabilizes the arrangement in which their two coordination sites occupy equatorial and an apical position.

• 
  PClF₄
• 
  PCl₂F₃
• 
  PCl₃F₂
• 
  PCl₄F

References