Enclathration of\nSaturated Five-Membered Rings by\nTricyclic Fused Host Systems

In this work, the\ntricyclic fused host systems <i>N</i>,<i>N′</i>-bis(9-phenyl-9<i>H</i>-xanthen-9-yl)butane-1,4-diamine\n(<b>H1</b>) and <i>N</i>,<i>N′</i>-bis(9-(naphthalen-1-yl)-9<i>H</i>-xanthen-9-yl)butane-1,4-diamine\n(<b>H2</b>) were investigated for their host potential for three\nsaturated five-membered ring guest solvents, namely, tetrahydrofuran,\ntetrahydrothiophene, and pyrrolidine (THF, THT, and PYRR). Both host\nspecies successfully enclathrated these solvents, forming 1:2 host–guest\ncomplexes with each one. Guest competition experiments by means of\nthe crystallization of <b>H1</b> from all combinations of equimolar\nguest mixtures demonstrated a host selectivity that increased in the\norder THT < PYRR < THF. However, analogous experiments with <b>H2</b> only revealed a consistent preference for THT, while the\nselectivity for THF and PYRR depended on the number and types of guest\nspecies present. Nonequimolar binary guest experiments were also carried\nout, and these largely concurred with observations made in the equimolar\nguest experiments. SCXRD analyses demonstrated that <b>H1</b> retained its preferred guest compound, THF, in the crystal of the\ncomplex by means of a classical hydrogen bond (H···O,\nN···O, 2.31(3) Å, 3.193(4) Å, and 162(3)°),\nwhile THT (least favored) was involved in weaker (host)C–H···S–C(guest)\nand (host)N–H···S(guest) interactions (H···S,\nC···S, 2.91, 3.836 Å, 164°; H···S,\nN···S, 3.112, 4.027 Å, 168.92°, and 3.045,\n3.971 Å, 174.65° for the two disorder guest components). <b>H2</b>, on the other hand, retained its preferred guest species\n(THT) in the complex by means of a singular short (guest)C–H···C–C(host)\ncontact (C···H, C···C, 2.83, 3.754 Å,\nand 156°) which was absent in the inclusion compound containing\ndisfavored THF. Moreover, also in this complex was identified a (host)N–H···S(guest)\nhydrogen bond (THF did not experience a hydrogen bond with <b>H2</b>); measurements were 3.468, 4.134 Å, and 135.38°. These\nobservations align exactly with the guest preferences of these two\nhost compounds. Hirshfeld surface considerations were employed to\nfurther explain these host behaviors in guest mixtures. Finally, thermal\nanalyses were undertaken in order to determine the relative thermal\nstabilities of these complexes.