Electronic Coupling in Mixed‐Valence Dinuclear Ferrocenes and Cobaltocenes with Saturated Bridging Groups

Abstract

We have synthesised a series of new dinuclear metallocenes [{M(Cp*)(C5H4)}2X] (Cp* = eta5-pentamethylcyclopentadienyl; M = Fe, Co, X = CMe2, SiMe2, GeMe2; M = Fe, X = Si2Me4). For the neutral dicobalt complexes, magnetic susceptibility measurements reveal intramolecular antiferromagnetic interactions of -21 and -14 cm(-1) for SiMe2- and GeMe2-bridged species, respectively, but negligible interaction for the CMe2-bridged compound. In contrast, intervalence charge-transfer (IVCT) data for the mixed-valence monocations of both Fe and Co complexes show electronic coupling to decrease in the order CMe2 > SiMe2 > GeMe2. This suggests that electronic coupling is principally through-space in contrast to results found from previous studies. The IVCT data also show much stronger coupling in the dicobalt species versus their diiron analogues.

Examination of the Mixed‐Valence State of the Doubly Boron‐Bridged Diferrocene Cation [(FeCp)2{μ‐C10H6(BPh)2}]+

“…, e = 58 m À1 cm À1 , a = 0.02; X = SiMe 2 , R= Me in THF, [25] n = 7480 cm À1 , e = 87 m À1 cm À1 , a = 0.024-0.039). An IVCT band has also been reported for the zwitterion BFc III at 4550 cm À1 in CH 2 Cl 2 , [31] but no further band analysis was performed.…”

“…[10] We observe that for both counterions (Dn 1/2 ) obs is somewhat larger than the value of predicted (Dn 1/2 ) calcd , a phenomenon that has been commonly observed for Class II and also for borderline Class I/II MV diferrocenium cations. [15,25,49] By using Hush theory, the interaction parameter a (a 2 % 4.24 10…”

“…[4,9,10] As such, these species are assigned to Class II based on the Robin and Day classification, [10,11] which is consistent with fast electron transfer that involves a double-well potential surface. Similarly, in the presence of small p-conjugated organic spacer units (A; X= vinylene, ethynylene, phenylene) Class II behavior is observed, [12][13][14][15][16][17][18][19][20] whereas longer spacers, [21] nonconjugated carbon, [17] or heteroatom spacers (e.g., Si, Ge, Sn, P, S, Se) [17,[22][23][24][25] generally lead to more weakly communicating systems (Class I or borderline Class I/II). Extensive studies have also been performed on the respective polymeric derivatives with heteroatom bridges.…”

Electronic Structure and Absorption Spectra of Biferrocenyl and Bisfulvalenide Diiron Radical Cations: Detection and Assignment of New Low‐Energy Transitions

“…On the basis of their tremendous impact on this research area, Fe II -Fe III bimetallocenes [1][2][3][4][5][6][7][8] can in fact be considered as the organometallic counterparts of the Creutz-Taube ion. A phenomenon that is exclusively associated with this class of compounds and that has aroused considerable interest over the years is the transition from a charge-localized state at low temperatures to a delocalized state at higher temperatures.…”

“…[1][2][3][4][5][6][7][8] In the solid state, Fc 2 I 3 is charge localized between 4.2 and 300 K, and exhibits two discrete quadrupole doublets Abstract: UV-visible/near-IR (NIR)/ mid-IR (MIR) solution, solid-state, and matrix-isolation electronic absorption spectra of the Fe II -Fe III mixed-valent homobimetallic compounds biferrocenyl triiodide (1) and 1',1'''-diethylbiferrocenyltriiodide (2) reveal the presence of a low-energy transition in the MIR region that has not been reported before. The new absorption feature and the known NIR band are both assigned to intervalence charge-transfer (IVCT) transitions.…”