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).

Molecular Structure and Magnetic and Optical Properties of Endometallonitridofullerene Sc3N@Ih‐C80 in Neutral, Radical Anion, and Dimeric Anionic Forms

“…Although the use of co‐crystallization agents such as M(OEP) (M = metal; OEP = octaethylporphyrin) is very popular for nitride clusterfullerenes, the ordering of Sc 3 N@C 80 molecules in xylene solvates shows that interaction with solvent molecules may already provide a sufficient ordering effect . The results of this work are in line with those earlier findings and demonstrate that a network of o ‐dichlorobenzene ( o ‐DCB) molecules around the fullerene cage (Figure a) can impose a completely ordered position of the carbon cage in 1 .…”

Supramolecular Inclusion Complexes of Two Cyclic Zinc Bisporphyrins with C60 and C70: Structural, Thermodynamic, and Photophysical Characterization

“…We also envisaged that the ortho ‐methyl groups of the mesityl substituents could engage in additional CH–π interactions with bound fullerene and increase the van der Waals contacts in the complex. The synthesis of the two macrocyclic bisporphyrin receptors, 1⋅ Zn 2 and 2⋅ Zn 2 , employed in this study has recently been described by us 20. The synthetic strategy relies on the macrocyclic templated dimerization of trans ‐ 3⋅ Zn mediated by the oxidative coupling of its terminal alkyne groups under Hay reaction conditions 21.…”

“…Recently, we reported the formation of thermodynamically stable inclusion complexes in solution of two macrocyclic bisporphyrins, 1⋅ Zn 2 and 2⋅ Zn 2 , with Sc 3 N@C 80 20. UV/Vis and fluorescence titration experiments confirmed the existence of strong π–π interactions between the fullerene and the flexible bisporphyrin dimer with hexyl spacers, 2⋅ Zn 2 .…”

Metallosupramolecular receptors for fullerene binding and release

“…Cyclic covalent receptors were synthesized by dimerization of two non-b-pyrrole-substituted monoporphyrins, bearing four meso-aryl substituents (7), to give 8 (Fig. 29 The association constant between fullerenes and porphyrins dramatically increased when using porphyrin dimers (vide supra) instead of a single porphyrin. 21 Subsequently, hydrogenation of 8 afforded the flexible cyclic dimer 9.…”

“…Würthner used FeX 2 salts (X = BF 4 À , CF 3 SO 3 À ) to link perylene bisimide (PBI) dyes, containing 2,2 0 -bipyridine groups (29), in order to prepare a M 4 L 6 tetrahedral structure 30 (Fig. Würthner used FeX 2 salts (X = BF 4 À , CF 3 SO 3 À ) to link perylene bisimide (PBI) dyes, containing 2,2 0 -bipyridine groups (29), in order to prepare a M 4 L 6 tetrahedral structure 30 (Fig.…”