Molecular π-magnets based on single organic molecules have attracted
increasing attention for their potential applications in optoelectronics and
spintronics. Global aromaticity in conjugated macrocyclic polyradicaloids is still
an open question that has only been tackled in molecules with an even number
of electrons. Here, we report the on-surface synthesis of a cyclopenta-ringfused
oligo(m-phenylene) macrocycle, 9MC, with an odd number of electrons.
The generated polyradicaloid undergoes a surface-induced distortion to a D3h
symmetry with a fully delocalized doublet ground state. Interestingly, 9MC
exhibits two aromatic annulene-within-an-annulene (AWA) ring currents in the
inner and outer rings.
more »
« less
This content will become publicly available on June 1, 2025
The anti-aromatic dianion and aromatic tetraanion of [18]annulene
π-Conjugated macrocycles behave differently from analogous linear chains because their electronic wavefunctions resemble a quantum particle on a ring, leading to aromaticity or anti-aromaticity. [18]Annulene, (CH)18, is the archetypal non-benzenoid aromatic hydrocarbon. Molecules with circuits of 4
- Award ID(s):
- 2003411
- PAR ID:
- 10517915
- Publisher / Repository:
- Nature
- Date Published:
- Journal Name:
- Nature Chemistry
- Volume:
- 16
- Issue:
- 6
- ISSN:
- 1755-4330
- Page Range / eLocation ID:
- 998 to 1002
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
more » « less
Abstract A new concept in anionic 10 π aromaticity is described by the embedding of a compensating charge within an aromatic cyclononatetraenide ring by the symmetric superposition of an alkyl ammonium bridge. This is accomplished by the methylation of azatriquinacene to give a quaternary ammonium salt, followed by oxidation to the tetraene and final deprotonation. The resulting zwitterion is a stable [9]annulene with strong aromaticity as shown by its degree of C−C bond equalization and a nucleus‐independent chemical shift value lower than that of benzene. The solid‐state structure shows an eclipsed stacking motif with the electron‐poor ammonium methyl groups occupying the electron‐rich cavity of the aromatic bowl.
-
more » « less
Abstract A new concept in anionic 10 π aromaticity is described by the embedding of a compensating charge within an aromatic cyclononatetraenide ring by the symmetric superposition of an alkyl ammonium bridge. This is accomplished by the methylation of azatriquinacene to give a quaternary ammonium salt, followed by oxidation to the tetraene and final deprotonation. The resulting zwitterion is a stable [9]annulene with strong aromaticity as shown by its degree of C−C bond equalization and a nucleus‐independent chemical shift value lower than that of benzene. The solid‐state structure shows an eclipsed stacking motif with the electron‐poor ammonium methyl groups occupying the electron‐rich cavity of the aromatic bowl.
-
more » « less
Abstract The dianion and dication of tetramesityl‐substituted tetracyclopentatetraphenylene, a circulene consisting of alternating five‐ and six‐membered rings, have been generated by reduction with alkali metals and oxidation with antimony(V) halides, respectively. They are theoretically predicted to adopt double annulenoid structures called annulene‐within‐an‐annulene models in which the outer and inner conjugation circuits are significantly decoupled. The theoretical structures were experimentally proven by X‐ray crystallographic analyses and the electronic configurations were supported by MCD spectra. Based on the13C NMR chemical shifts, negative and positive charges are shown to be located mainly at the outer periphery, indicating that the dianion and dication have delocalized 22‐π and 18‐π electron outer perimeters, respectively, and 8‐π electron structure at the inner ring. Notably, the dianion has an open‐shell character, whereas the dication has a closed‐shell ground state.
-
more » « less
Abstract The dianion and dication of tetramesityl‐substituted tetracyclopentatetraphenylene, a circulene consisting of alternating five‐ and six‐membered rings, have been generated by reduction with alkali metals and oxidation with antimony(V) halides, respectively. They are theoretically predicted to adopt double annulenoid structures called annulene‐within‐an‐annulene models in which the outer and inner conjugation circuits are significantly decoupled. The theoretical structures were experimentally proven by X‐ray crystallographic analyses and the electronic configurations were supported by MCD spectra. Based on the13C NMR chemical shifts, negative and positive charges are shown to be located mainly at the outer periphery, indicating that the dianion and dication have delocalized 22‐π and 18‐π electron outer perimeters, respectively, and 8‐π electron structure at the inner ring. Notably, the dianion has an open‐shell character, whereas the dication has a closed‐shell ground state.
