Mixed-valent ferrocenyltellurenyl halides. Synthesis, electrochemistry and unusual molecular structure

Halogenation of diferrocenyl ditelluride (Fc2Te2) allowed corresponding isostructural ferrocenyltellurenyls [FcTeX] (X= Cl (6), Br (7), X = I (8)). Their molecular structures in the solid state confirm them to be mixed-valent FcTe–TeX2Fc, however, the single band in 125Te NMR spectrum of 8 and electrochemical data suggests the monomeric [FcTeX] structure in the solution at room temperature. Remarkable bent of non-halogenated atom of Te towards the Fe atom observed in the solid state structures of 6–8, removes the Te atom from the plane of the related Cp ring (15°–20°) and may indicate the interaction of filled nonbonding 3d orbitals of Fe with the appropriate Te localized LUMO.