The (<i>E</i>)-2-Ferrocenylethenylcobaltocenium Cation. A Missing Link in Heteronuclear Bimetallocene-Based Donor−Acceptor Conjugate Chemistry Exhibiting Irregular Solvatochromism

The new heteronuclear ethene-bridged bimetallocene ferrocenylethenylcobaltocenium cation (fec-ene-coc+), as hexafluorophosphate and chloride, was prepared by Knoevenagel condensation of methylcobaltocenium PF6 and ferrocenecarbaldehyde. The chloride was obtained by anion exchange. X-ray crystal structure, cyclic voltammetry, and detailed solvatochromism data are reported and compared to those of related bimetallocenes, namely, the ethyne-bridged fec-yne-coc+, the directly linked fec-coc+, the new ethene-bridged ruc-ene-coc+, and the ethyne-bridged ruc-yne-coc+, as well as related termetallocenes.