title: Stabilization of cucurbituril/guest assemblies via long-range Coulombic and CH···O interactions.
abstract: Cucurbit[n]urils (CB[n], n = 6-8) interact strongly with metal-bound 4'-substituted terpyridine ligands (M = Fe(II) and Ir(III)) via CH···O hydrogen bonding, despite significant separation between the positive metallic cation and the carbonylated rim of CB[n], and the location of the latter in the second coordination sphere of the metal ion. While water has been shown to mediate interactions between cations and CB[n]s in some assemblies, mediation by organic ligands is unprecedented. The recognition process is driven by the contrasted combination of extremely favorable binding enthalpies (up to 20.2 kcal/mol) and very unfavorable entropic components (as low as -10.2 kcal/mol). Dynamic oligomers were prepared in the presence of CB[8], which acts as a "soft", noncovalent linker between metal/terpyridine complexes, and interconnects two 4'-substituents inside its cavity. Social self-sorting between CB[8] and metal/terpyridine complexes bearing 4'-(2-naphthyl) and 4'-(2,3,5,6-tetrafluorophenyl) substituents was also observed, and could afford well-organized oligomers with alternating Fe(II) and Ir(III) cations.
authors.affiliation: Department of Chemistry and Biochemistry, Ohio University , Athens, Ohio 45701, United States.
authors.forename: Roymon
authors.initials: R
authors.lastname: Joseph
authors.forename: Anna
authors.initials: A
authors.lastname: Nkrumah
authors.forename: Ronald J
authors.initials: RJ
authors.lastname: Clark
authors.forename: Eric
authors.initials: E
authors.lastname: Masson