Phosphonitrilic Compounds. III.1 Molecular Inclusion Compounds of Tris(o-phenylenedioxy)phosphonitrile Trimer

Tris(o-phenylenedioxy)phosphonitrile trimer forms crystalline inclusion compounds when recrystallized from organic solvents. Similar adducts are formed by an unusual spontaneous inclusion process, accompanied by a change in crystal structure, which occurs when the solid is brought into contact with the liquid or vapor of many organic compounds. For these adducts, the ratio of host to guest compound depends on the molecular dimensions of the included species. In specific cases, one included compound can be displaced from the adduct by another, and selective absorption from mixed liquids also takes place. X-Ray single crystal and powder diffraction data suggest that at 25° the pure phosphonitrilic compound exists as a monoclinic or triclinic structure with an eight-molecule unit cell. In the adduct form, the material exists as a hexagonal structure which contains two molecules of phosphonitrilic compound and generally not more than one included molecule. The mode of crystal packing is discussed, and the results are interpreted in terms of clathrate or channel-compound formation.