Enclathration of Saturated Five-Membered Rings by Tricyclic Fused Host Systems

In this work, the tricyclic fused host systems N,N′-bis(9-phenyl-9H-xanthen-9-yl)butane-1,4-diamine (H1) and N,N′-bis(9-(naphthalen-1-yl)-9H-xanthen-9-yl)butane-1,4-diamine (H2) were investigated for their host potential for three saturated five-membered ring guest solvents, namely, tetrahydrofuran, tetrahydrothiophene, and pyrrolidine (THF, THT, and PYRR). Both host species successfully enclathrated these solvents, forming 1:2 host–guest complexes with each one. Guest competition experiments by means of the crystallization of H1 from all combinations of equimolar guest mixtures demonstrated a host selectivity that increased in the order THT < PYRR < THF. However, analogous experiments with H2 only revealed a consistent preference for THT, while the selectivity for THF and PYRR depended on the number and types of guest species present. Nonequimolar binary guest experiments were also carried out, and these largely concurred with observations made in the equimolar guest experiments. SCXRD analyses demonstrated that H1 retained its preferred guest compound, THF, in the crystal of the complex by means of a classical hydrogen bond (H···O, N···O, 2.31(3) Å, 3.193(4) Å, and 162(3)°), while THT (least favored) was involved in weaker (host)C–H···S–C(guest) and (host)N–H···S(guest) interactions (H···S, C···S, 2.91, 3.836 Å, 164°; H···S, N···S, 3.112, 4.027 Å, 168.92°, and 3.045, 3.971 Å, 174.65° for the two disorder guest components). H2, on the other hand, retained its preferred guest species (THT) in the complex by means of a singular short (guest)C–H···C–C(host) contact (C···H, C···C, 2.83, 3.754 Å, and 156°) which was absent in the inclusion compound containing disfavored THF. Moreover, also in this complex was identified a (host)N–H···S(guest) hydrogen bond (THF did not experience a hydrogen bond with H2); measurements were 3.468, 4.134 Å, and 135.38°. These observations align exactly with the guest preferences of these two host compounds. Hirshfeld surface considerations were employed to further explain these host behaviors in guest mixtures. Finally, thermal analyses were undertaken in order to determine the relative thermal stabilities of these complexes.