Möbius Aromatic [28]Hexaphyrin Germanium(IV) and Tin(IV) Complexes: Efficient Formation of Triplet Excited States.

[28]Hexaphyrin GeIV and SnIV complexes were synthesized in high yields by reactions of [28]hexaphyrin with GeCl4 or SnCl4 in the presence of triethylamine. Both complexes display distinct 28π Möbius aromatic character and possess a trigonal bipyramidal geometry at the central GeIV or SnIV atom. The equatorial hydroxy group of the GeIV complex was smoothly exchanged with neutral nucleophiles, such as phenol derivatives and thiophenol, with retention of configuration. In the SnIV complex, intersystem crossing to the T1  state is remarkably enhanced owing to the effective heavy-atom effect, thus allowing the formation of the T1  state in high yield. The T1  states of the GeIV and SnVI complexes were found to be antiaromatic on the basis of the transient absorption features in line with the Baird rule.