Secondary bonding. Part 1. Crystal and molecular structures of (C6H5)2 IX (X = Cl, Br, or I)

The structures of the title compounds have been determined. The three compounds are isomorphous, monoclinic, space group C2/c, Z= 8, with the following cell constants and R values: [graphic omitted] In the dimeric structures Ph2I(µ-X)2Iph2 mean bond lengths are I–C 2.09, i–Cl 3.09, I–Br 3.25, and I–I 3.44 Å, The I–X bonds are each 0.77 Å longer than in the corresponding IX gas, indicating bond orders of about 0.35. The bonding is interpreted in terms of secondary bonds (I ⋯ X). holding [Ph2I]+ and X– units together.