A new host for polymer and small-molecule clathration

The synthesis and inclusion properties of a new clathration host, tris(3,6-dimethylphenylenedioxy)cyclotriphosphazene, is described. The guest-free structure has a triclinic unit cell, space group P1̄, with unit cell dimensions a = 9.418(1) Å, b = 17.887(4) Å, c = 8.036(2) Å, α = 95.50(2)°, β = 100.57(1)°, and γ = 95.58(1)°. Recrystallization of the host from dioxane or from a poly(tetramethylene oxide)/benzene mixture afforded two different guest-included structures. The tris(3,6-dimethylphenylenedioxy)cyclotriphosphazene-dioxane inclusion adduct crystallizes in a monoclinic system, space group P2₁/c, with unit cell dimensions a = 9.3481(1), b = 19.6569(1), c = 16.4099(3), and β = 97.351(1)°. The guest occupies a cagelike void located between the phosphazene rings. The poly(tetramethylene oxide) adduct crystallizes in a hexagonal system, space group P6₃/m, with unit cell dimensions a = 11.4902(2) Å and c = 13.3138(3) Å. In this case, the polymeric guest is located in tunnels created along the c-axis. Adduct formation also occurs between tris(3,6-dimethylphenylenedioxy)cyclotriphosphazene and other cyclic, linear, and polymeric species such as tetrahydrofuran, methylene chloride, polyethylene, and cis-polybutadiene. Thermogravimetric analysis and differential scanning calorimetry were used to characterize the thermal behavior of the inclusion adducts. Crystal engineering of these spirocyclotriphosphazene hosts is facilitated by the ease in which the void and tunnel diameter can be tailored by systematic adjustments to the size and nature of the side group.