$\ce{I2Cl6}$ is a dimer of $\ce{ICl3}$. $\ce{ICl3}$ is T-shaped, with $\ce{I}$ being $\mathrm{sp^3d}$ and having two lone pairs.
I read in Inorganic Reaction Mechanisms by R. K. Sharma that $\ce{I2Cl6}$ is formed by the extra two $\ce{Cl-I}$ bridge bonds. What I don't understand is, why does the bridge bond form? And is it a coordinate bond or something like a banana bond (as in $\ce{B2H6}$)?
Source: Sharma, R. K. Inorganic Reaction Mechanisms; Discovery Publishing House: 2007.
