Medium-sized cyclic oligomeric phosphazenes [PCl2N](m) (where m = 5-9) that were prepared from the reaction of PCl5 and NH4Cl in refluxing chlorobenzene have been isolated by a combination of sublimation/extraction and column chromatography from the predominant products [PCl2N](3) and [PCl2N](4). The medium-sized rings [PCl2N](m) have been characterized by electrospray ionization mass spectroscopy (ESI-MS), their P-31 chemical shifts have been reassigned, and their T-1 relaxation times have been obtained. Crystallographic data has been recollected for [PCl2N](5), and the crystal structures of [PCl2N](6), and [PCl2N](8) are reported. Halogen-bonding interactions were observed in all the crystal structures of cyclic [PCl2N](m) (m = 3-5, 6, 8). The crystal structures of [P(OPh)(2)N](7) and [P(OPh)(2)N](8), which are derivatives of the respective [PCl2](m) are also reported. Comparisons of the intermolecular forces and torsion angles of [PCl2N](8) and [P(OPh)(2)N](8) with those of three other octameric rings are described. The comparisons show that chlorophosphazenes should not be considered prototypical, in terms of solid-state structure, because of the strong influence of halogen bonding.