 The apparent coordination number of five, or even six, associated with the carbon atom at the top of the pyramid is a rarity as compared to the usual maximum of four.Studying these cations was sparked, at the time, by amazing results in computational chemistry.While calculating the optimal geometry of the mono-cation which arises from the extraction of chloride from 3-chlorotricyclo[2.1.0.02,5]pentane, the three bridges were expected to orient in space with angles of roughly 120°.