Halogen-Molecule Bridges in Solid Addition Compounds

Abstract

ONE very striking result obtained from X-ray work on solid addition compounds in which halogen molecules act as electron acceptors is the fact that both halogen atoms of a particular Hal₂ molecule may simultaneously be linked to donor molecules. Thus, in the 1 : 1 compounds formed by 1,4-dioxan and bromine (or iodine) endless chains are present which are built up of alternating dioxan and halogen molecules and containing linear O—Hal—Hal—O arrangements¹. Moreover, in the solid 1 : 1 compound formed by benzene and bromine, straight chains of alternating benzene and bromine molecules have been established²; the benzene-ring planes are parallel and the bromine molecules symmetrically arranged on the common chief axis of the benzene rings. Until quite recently it was uncertain whether more than one single halogen-molecule bridge could actually start from one particular electron donor atom. In the case of oxygen and other donor atoms possessing more than one lone electron pair such an arrangement would not appear to be impossible.