Halogen−ethynyl interaction mimicry and the role of halogen trimer synthon (X···X)3 in crystal packing have been discussed in several papers. However, the ethynyl trimer motif (C⋮C−H···C⋮C)3 has not been systematically studied in crystal engineering. The (C⋮C−H···C⋮C)3 synthon is reproduced in 10 isostructural host−guest crystalline adducts in the R3 space group. Not only are the ethynyl structures (4-EPOT) identical to the iodo series (4-IPOT) because of deliberate design but they also show tighter guest inclusion due to the stronger C⋮C−H···π hydrogen bond compared to the I···I interaction. 4-EPOT−guest inclusion adducts are more stable than 4-IPOT inclusion compounds on the basis of Cerius2 lattice energy computations (ΔE = ∼8 kcal mol-1). The temperature for guest release in thermal gravimetric analysis from the 4-EPOT−host framework is higher than the solvent boiling point (Tonset − Tbp) by as much as 123 °C for CH2Cl2, 103 °C for C6F6, and 83 °C for Et2O. The guest molecules are included in the hos...