A new host compound TTPP (tris(2,3-triphenylenedioxy)cyclotriphosphazene), which is able to form a porous network, has been synthesized in five steps. When it crystallizes as a single component, TTPP exhibits a crystal structure with a monoclinic unit cell, the space groupP2₁/c (no. 14) and unit cell dimensions of a = 14.909(2) Å, b = 31.013(4) Å, c = 9.074(1) Å, β = 102.12(1)°. Co-crystallization of TTPP with 1,2,4-trichlorobenzene forms an inclusion crystal having a triclinic unit cell with a P space group (no. 2) and unit cell dimensions of a = 8.769(2) Å, b = 15.024(2) Å, c = 21.216(2) Å, α = 94.82(0)°, β = 99.98(0)°, γ = 98.23(1). The guest lies in two kinds of channel-like cavities with dimensions of 6.1 × 8.4 Ų and 10.7 × 12.4 Ų respectively. This represents the biggest porous network built up by spirocyclotriphosphazene derivatives to date.