The isolation of nitrilohexaphosphonitrilic chloride is reported in this work, and its structure shown to be a tricyclic condensed ring. The physical and chemical properties of this molecule are unlike the monocyclic phosphonitrilic chlorides. The reasons for this are not fully understood, but are thought to involve the weakness of the central P-N bond; the crystal structure and mass spectrum of the molecule show that this central bond is long and weak. Substitution reactions, common in the monocyclic chlorides, bring about either a partial or total break-down of the tricyclic P₆N₇ skeleton. In the case of electron-withdrawing substituents (e.g. -F,OMe), complete loss of the phosphonitrilic skeleton is achieved, and, in the case of electron-donating groups (-NMe₂), substitution onto the ring brings about cleavage of one of the internal P-N bonds. The molecule that is formed during the dimethylamination of P₆N₇Cℓ₉ is unique in phosphonitrilic chemistry and its suggested structure visually emphasizes the weakness of the central P-N bond in P₆N₇Cℓ₉. A series of molecular orbital calculations on the P₆N₇Cℓ₉ molecule were carried out in this study, and it is suggested that the observed structural trends in the molecule can be attributed to the properties of the phosphorus 3d[subscript]yz orbital on the bridgehead atoms. / Science, Faculty of / Chemistry, Department of / Graduate