Solid Fluorine and Solid Chlorine: Crystal Structures and Intermolecular Forces

Extended Hückel molecular-orbital (EHMO) calculations and molecular multipole sums are compared for various assemblies of Cl2 molecules. It is shown that the multipole sums does not predict the correct space group for Cl2 but that the EHMO calculation does, if there is d-orbital involvement. Some comments are made on the crystal structures of α- and of β-F2, both different from those of the other halogens.