title: Complexation of Sc3N@C80 endohedral fullerene with cyclic Zn-bisporphyrins: solid state and solution studies.
abstract: We report the synthesis of two cyclic β-pyrrole unsubstituted meso-tetraphenyl bisporphyrins in which the porphyrin units are connected by two 2,3-hexadiynyl-1,6-dioxo or two hexyl-1,6-dioxo spacers, respectively. Both cyclic porphyrin dimers exist in solution as mixtures of two conformational isomers. In the solid state, the receptor with diynyl spacers forms a 1:1 complex with the icosahedral (I(h)) isomer of the trimetallic nitride endohedral fullerene Sc(3)N@C(80). In this complex the receptor adopts a scoop-shaped conformation having a dihedral angle of 87.25° between the two porphyrin planes. The hexyl spaced analogue, however, adopts a similar conformation upon encapsulation of one molecule of Sc(3)N@C(80) in a self-assembled dimeric capsule. The capsular complexes pack in columns and render the fullerene units completely isolated. In toluene solution, (1)H NMR experiments indicate that the endohedral fullerene Sc(3)N@C(80) is exclusively bound by the expanded isomer of both dimers. UV-vis and fluorescence titration experiments confirmed the existence of strong π-π interactions between the fullerene Sc(3)N@C(80) and the flexible bisporphyrin dimer with hexyl spacers. At micromolar concentration, the flexible receptor forms only a 1:1 complex with the endohedral fullerene with stability constant value of K(a) = 2.6 ± 0.3 × 10(5) M(-1).
authors.affiliation: Institute of Chemical Research of Catalonia (ICIQ), Avgda. Països Catalans 16, 43007 Tarragona, Spain.
authors.forename: Laura P
authors.initials: LP
authors.lastname: Hernández-Eguía
authors.forename: Eduardo C
authors.initials: EC
authors.lastname: Escudero-Adán
authors.forename: Julio R
authors.initials: JR
authors.lastname: Pinzón
authors.forename: Luis
authors.initials: L
authors.lastname: Echegoyen
authors.forename: Pablo
authors.initials: P
authors.lastname: Ballester