Formed between two different halogens. The larger (less electronegative) halogen is the central atom. Types: XX' (ClF, ICl), XX'3 (ClF3, BrF3, ICl3), XX'5 (BrF5, IF5), XX'7 (IF7 only). Geometries by VSEPR: XX' = linear; XX'3 = T-shaped (2 lone pairs in equatorial); XX'5 = square pyramidal (1 lone pair); XX'7 = pentagonal bipyramidal (0 lone pairs). More reactive than constituent halogens. ICl and IBr are used as iodinating agents. ClF3 is extremely reactive — ignites asbestos and water. IF7 is the only XX'7 compound because I is large enough to accommodate 7 F atoms.