Electronic communication in oligonuclear ferrocene complexes with anionic four-coordinate boron bridges

Linda Kaufmann, Jens-Michael Breunig, Hannes Vitze, Frauke Schödel, Israel Nowik, Markus Pichlmaier, Michael Bolte, Hans-Wolfram Lerner, Rainer F. Winter, Rolfe H. Herber, Matthias Wagner
2009 Dalton Transactions  
The di-and trinuclear ferrocene species Li[Fc-BPh 2 -Fc) (Li[9)) and Li 2 [Fc-BPh 2 -fc-BPh r Fc) (Li 2 [1O)) have been investigated with regard to their electrochemical properties and the degree of intervalence charge-transfer after partial oxidation. Li[9) shows two distinct one-electron redox waves for its chemically equivalent ferrocenyl substituents in the cyclic voltammogram (EI I2 = -0.38 V, -0.64 V; vs. FcH/FcH+). The corresponding values of Li 2 [lO) are E II2 = -0.45 V (two-electron
more » ... 5 V (two-electron process) and -I. 18 V. All these redox events are reversible at r. t. on the time scale of cyclic voltammetry. X-ray crystallography on the mixed-valent Fell 2 FellI complex Li(l2-c-4MIO) reveals the centroid-centroid distance between the cyclopentadienyl rings of each of the terminal ferrocenyl substituents (3.329 A) to be significantly smaller than in the central I, I' -ferrocenediyl fragment (3.420 A). This points towards a charge-localized structure (on the time scale of X-ray crystallography) with the central iron atom being in the FellI state. M613bauer spectroscopic measurements on Li(12-c-4MIO) lend further support to this interpretation . Spectroelectrochemical measurements on Li[9) and Li2[lO) in the wavelength range between 300-2800 nm do not show bands interpretable as intervalence charge-transfer absorptions for the mixed-valent states. All data accumulated so far lead to the conclusion that electronic interaction between the individual Fe atoms in Li[9) and Lh[IO) occurs via a through-space pathway and/or is electrostatic in nature.
doi:10.1039/b821406a pmid:19352521 fatcat:fl7psltpzfcojcwmaizdpofnri