Although extremely reactive, ClF5 is a well-characterized cmpd.
Cl (and Br) however do not form an analogue of IF7 (pentagonal
The reason for this is either steric or electronic. Consider each in turn
and come up with both a steric an electronic reason for the instability of
ClF7. In particular, how do the np-nd energy gaps behave as one goes from
Cl right arrow Br right arrow I?
(Hybridization is now thought to be an artifact and the term should be avoided.)
"I believe the chemical bond is not so simple as some people seem to think."
Robert S. Mulliken