Two forms of interdigitated layered arrangements of C-pentylpyrogallol[4]arene (PgC(5)) have been structurally elucidated and show variations in packing arrangements and host guest interactions. Molecular dynamics simulations reveal a propensity for formation of self-included dimers, with or without incorporated solvent. Combined gas sorption and PXRD results show the presence of seven forms of PgC(5), with and without CO2 (and their interconversions). This is the first CO2 gas sorption study of pyrogallol[4]arenes, and it provides evidence that pyrogallol[4]arenes may act as frustrated organic solids.