The nitrogen centres of hexachlorophosphazene are weakly basic, and this Lewis base behaviour has been suggested to play a role in the polymerisation mechanism. Specifically, hexachlorophosphazene has been reported to form adducts of various stoichiometries with Lewis acids Aluminium chloride|, Aluminium bromide|, Gallium trichloride|, Sulfur trioxide|, Tantalum(V) chloride|, Vanadium oxytrichloride|, but no isolable product with Boron trichloride|.
Among these, the best structurally characterised are the 1:1 adducts with aluminium trichloride or with gallium trichloride; they are found with the Al/Ga atom bound to a N and assume a more prominently distorted chair conformation compared to the free hexachlorophosphazene. The adducts also exhibit fluxional behaviour in solution for temperatures down to −60 °C, which can be monitored with N and P-NMR.