Mixed-Valence Biferrocenium Salts of Xn–TCNQ (X = F, Cl; n = 1, 2): Correlation between Molecular Structures and Assembled Structures



Charge-transfer salts composed of biferrocene derivatives and Xn–TCNQ (X = F, Cl; n = 1, 2; TCNQ = tetracyanoquinodimethane) were prepared and crystallographically characterized. All nine salts exhibited a 1:2 donor/acceptor (D/A) ratio consisting of mixed-valence biferrocenium cations and anions with acceptor dimers. The packing patterns were correlated to the donor substituents. On the basis of the π–π interactions of the cations, the observed structures were classified into three categories: segregated-stack structures for the biferrocenium and dibromo-biferrocenium salts, mixed-stack structures [···(DA2)n···] for the diiodo-biferrocenium salts, and intermediate structures [···(DDA2A2)n···] for the bromo-biferrocenium salts.