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MÖSSBAUER SPECTROSCOPIC STUDY ON THE MIXED AND AVERAGED VALENCE FERROCENE
DERIVATIVES
M. Watanabe, S. Iijima, I. Motoyama, H. Sano
To cite this version:
M. Watanabe, S. Iijima, I. Motoyama, H. Sano. MÖSSBAUER SPECTROSCOPIC STUDY ON
THE MIXED AND AVERAGED VALENCE FERROCENE DERIVATIVES. Journal de Physique
Colloques, 1979, 40 (C2), pp.C2-392-C2-394. �10.1051/jphyscol:19792136�. �jpa-00218508�
JOURNAL DE PHYSIQUE Colloque C2, suppl&ment au n o 3, Tome 40, mars 1979, page C2-392
MOSSBAUER S P E C T R O S C O P I C S T U D Y ON THE M I X E D AND AVERAGED VALENCE FERROCENE D E R I V A T I V E S
M. Watanabe, S. Iijima, I. Motoyama and H. Sano
Department o f Chemistry, FaeuZty o f Science, Tokyo MetropoZitan University, Fukasava, Setagaya, Tokyo, Japan 158.
RCsum6.- Les monocations de diferocenylacCtylSne et de 12.21 ferrocdnophane-1,13-diyne ont 6tB 6tu- digs au moyen de la spectroscopie Mgssbauer et d'autres mesures physiques. Les rgsultats de t46ssbauer ont clairement montrd que la forme du cation est d'un type de valence multiple et que celle du
p.g
ferroc6nophane-1,13-diyne est d'un type de valence moyenne. Les rdsultats prdcddents sont compards 1 ceux obtenus 2 partir de dgrivbs du ferrocPne, ddjP connus, ces derniers ayant des valences multiples et moyennes.
Abstract
.-
Monocations of diferocenylacetylene and t 2 . 2 1 f errocenophane-1 ,13-diyne were studied by means of Miissbauer spectroscopy and other physical measurements. The Miissbauer results have clearly shown that the former cation is of the mixed valence type and the latter is of the averaged valence type. The above results are discussed in comparison with those of the mixed and averaged valence ferrocene derivatives previously reported.Cowan /I/.and Hendrickson /2/ reported that there are intramolecular interactions between iron atoms in the mixed valence cations of biferrocene (I) and biferrocenylene (11) and that the averaged valence state is found in the latter. The question, however, remains as to whether the strong interac- tion in biferrocenylenium cation is ascribed to di- rect metal-metal interaction or to the interaction
.
through the a-system of fused fulvalene ligands. For the purpose of making this point clear, acetylenic ferrocene derivatives, such as diferocenylacetylene
(111) and r2.21 ferrocenophane-l,13-diyne (IV), have been investigated by means of Mgssbauer and electro- nic spectroscopy and cyclic voltammetry.
1. Experimental.- Diferrocenylacetylene (111) /3/
and L2.23 f errocenophane- I , 13-diyne (IV) 141 were prepared according to the method previously reported and led to the corresponding monocations by action of iodine on them in benzene. All the compounds used in this study were identified by means of the ele- mental analysis. The Mgssbauer spectra were measured
against a 57~o(~t) source moving in a constant acce- leration mode at room temperature. The velocity sca- le was normalized with respect to metallic iron.
Electronic absorption spectra were measured in solu- tion using acetonitrile as the solvent with a Hita- chi spectrometer model EPS-3T. Cyclic voltammograms were measured at a stationary Pt electrode using a potentiostat model HA-101 and a functiongenerator model HB-107A.
2. Results and Discussion
.-
~gssbauer parameters of the compounds used in this study are listed in table I and Miissbauer spectra of diferrocenylacetylenium triiodide and L 2.g
ferrocenophane- ~ 3 - d i y n i u m quin- quiiodide are shown in figure 1.Tzble I : Miissbauer parameters of ferrocene and related compounds.
-- -
Compound Temperature QS-l IS (K) (mms ) (m.s-l) FCH
FCH' I ~ - FcCzCFc FCC=CFC+ I ~ -
FDA FDA' I ~ -
FCFC+ picrate- BFD' picrate-
*Reference / 1 /. Fc: ferrocenyl, FDA:
p.21
ferroce-nophane-1,13-diyne, BFD: biferrocenylene.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19792136
- 2 - 1 0 1 2 3 Velocity (mms'l )
Fig. 1 : Mgssbauer spectra at 78 K of t2.21 ferro- cenophane-l,l3-diynium quinquiiodide (top) and di- ferrocenylacetylenium triiodide (bottom). Velocity scale is shown with respect to metallic iron.
Diferrocenylacetylenium cation shows two qua- drupole s~littings doublets (QS : 2.18 mm s-', IS : 0.54 mm s-', QS : 0.49 mm s-l, IS : 0.50 mm s-' at 78 K). These values are different from those expect- ed for the structure having fixed ferrocene and ferricinium nucleus and are almost the same as those observed in the monocation of biferrocene (I). The fact suggests that there is weak interaction through the acetylenic TI-system between the iron atoms, which are not equivalent on the Miissbauer time scale,
10-'s.
On the other hand, the monocation of C2.21 ferrocenophane-1,13-diyne has only one quadrupole- split doublet (QS : 1.61 mm s-'
, ,
IS : 0.54 mm s-' at 78 K), which is substantially identical to that observed in the biferr~cen~lenium monocation. This observation clearly indicates that there is only one iron state on the6ssbauer time scale, and the oxi- dation state is neither that of ferrocene nor ferri- cinium ion, but the averaged valence state between these compounds. The averaging of oxidation state can be reasonably explained in terms of the strong metal-metal interaction through the conjugated TI-system, since the Fe-Fe distance (about 6.51)
in the acetylenic compound (IV) is too large to allow the direct metal-metal interaction. This explanation is supported by the fact that no averaged valence state was found even in the monocation of 1,12-dime- thy1[
ferrocenophane, which has a shorter Fe--
F; distance (4.6
2)
and no conjugated TI-system bet- ween the two ferrocene nuclei 151.~dditional evidence supporting the strong Fe- Fe interaction is also given by the spectral and electrochemical results. Mixed valence compounds ge- nerally have a characteristic absorption band in the near infrared region where neither the ferrocene
fIFe(111)-Fe(11~+ 161. All the monocations investi- gated in this study also have the corresponding absorption band in this region. B.27 ferrocenophane- 1,13-diynium quinquiiodide has an absorption (h '
max' 1 8 0 0 n m , ~ : 1250), which is similar to that of bi- ferrocenylenium tetrafluoroborate (Amax : 1550 nm, E : 2100), while diferrocenylacetylenium triiodide has a much weaker one (Amax : 1360 nm, E : 400). The interaction parameter between the iron atoms can be estimated using the following equation proposed by Hush /7/
where r is the distance separating the donor and acceptor in ~ n ~ s t r g m , dv2 is the band half-width in wave number, cmax is the molar absorptivity at the band maximum, v is the frequency in wave number. By using the equation, a2 is calculated to 2.3 x
(a : 0.048) for diferrocenylacetylenium triiodide, and 8.0 x (a : 0.090) for p.21 ferrocenophane
1,13-diynium quinquiiodide
.
The value of a2 for the latter is three to four times larger than that for the former. This is quite consistent with the results obtained in the ~Sssbauer spectroscopic study.The cyclic voltammograms of the compounds (111) and (IV) in CH2C12 containing n-BusNClOlr showed that two one-electron oxidation peaks (Elj2 : 0.94V, EM:
0.60 V) were given for the latter compound (IV), while one peak corresponding to two-electron oxida-
tion was given for the former (111). The results, which are in good accord with those reported by
Cowan 181, also suggest the presence of the strong metal-metal interaction in the monocation of the compound (IV)
.
On the basis of the results presented above, we can conclude as follows; the monocation of
II2.q
ferrocenophane-1,13-diyne (IV) is of the averaged valence type, as reported in the studies of monoca- tion of biferrocenylene (11), and the averaging is probably due to the electron-delocalization through the conjugated acetylenic linkage. On the other hand, the monocation of diferrocenylacetylene (111) is of the mixed valence, in which little averaging occurs in the oxidation state of iron atoms.
molecule nor the ferricinium ion has any absorption.
This absorption is assigned to an intervalence elec- tron-transfer transition, [Fe (11)-Fe(111u' ---+
JOURNAL DE PHYSIQUE
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