Guest-Exchange and Guest-Release via Gas–Solid Contact in Clathrate Crystals Based on 2,5-Bis(9-hydroxyfluoren-9-yl)thieno[3,2-b]thiophene as a Host Compound

The host compound 2,5-bis(9-hydroxyfluoren-9-yl)thieno[3,2-b]thiophene (1) afforded clathrate crystals represented by the formula (1)(guest)2 for the guests EtOH, n-PrOH, and i-PrOH. Their X-ray crystal analyses revealed that the host frameworks are isostructural. The guest molecules, which are embedded in a channel-type of host void, were exchanged with other guest species by vapor contact. Upon exposure of these crystals to methanol vapor, guest elimination was induced to give the guest-free host 1 crystal [β-form, P1-, a = 13.111(4), b = 13.724(3), c = 9.766(3) Å, α = 97.11(2), β = 98.64(3), γ = 64.56(2)°, V = 1565.3(8) Å3]. The crystal thus obtained is a polymorphic form of the guest-free 1 crystal which is obtained by recrystallization from dichloromethane [α-form, P21/n, a = 17.403(3), b = 20.654(4), c = 8.695(1) Å, β = 99.73(1)°, V = 3080.4(9) Å3]. Once the guest molecules have been lost, gas-sorptive enclathration was not accomplished for either of these polymorphic host crystals; host 1 does not act as an apohost.