Ferrocene compounds, Mossbauer

Figure 4. Mossbauer spectrum typically found for ferrocene compounds. Key IS, isomer shift ...

Other Papers.—Various iron species prepared by the vacuum pyrrolysis of acetyl-ferrocene-furfural resins at 400°C have been studied by Mossbauer spectroscopy. These consist of an amorphous glass-like carbon matrix containing free iron atoms, Fe+ ions, iron clusters, superparamagnetic iron, and ferromagnetic iron.333 The effect of pressure of up to 50kbar on the absorption spectra of five iron(m), two iron(n) and one mixed valence compound has been studied. In six of the compounds, but not in basic ferric acetate or soluble Prussian Blue, the observed pressure-induced bands were assigned to d-d transitions of converted iron(n) for the ferric compounds and to spin-forbidden d-d bands for the ferrous compounds. The charge-transfer band from iron(n) to iron(m) in soluble Prussian Blue showed a blue shift at pressures up to 7.2 kbar.334... 

A98. N. N. Greenwood and T. C. Gibb, Mossbauer Spectroscopy. Chapman Hall, London, 1971. Chapter 9, pp. 221-238 Covalent iron compounds (41), treats binary carbonyls, carbonyl anions, hydride anions, substituted iron carbonyls, ferrocene and other 7r-cyclopentadienyl iron derivatives. 

SB-containing ferrocene groups have received much attention in the late 1990s. Thus, [1 + 1] and [2 + 2] macrocycles and a variety of acyclic SB-containing ferrocene groups have been prepared by reaction of formyl- and l,l -diformylferrocene with the appropriate diamine or by condensation of aminomethylferrocene with (56a), (57a), or 3-methoxy-2-hydroxybenzaldehyde.41 The compounds have been characterized by IR, NMR, Mossbauer spectroscopy, and FAB mass spectroscopy. 

There is a large class of iron organometallic compounds which can be described as molecular, diamagnetic, and highly covalent. They are derived in the main from the parent compounds iron pentacarbonyl, Fe(CO)s, and the cyclopentadienyl complex ferrocene, (jr-CsHslaFe or CpaFe. In view of their large numbers, it is not surprising that considerable Mossbauer spectral data are available, but as we shall now see the interpretation of this data introduces considerable problems. 

Although the Mossbauer spectra of the sandwich compounds are insensitive to ring substitution, a wide range of parameters is observed for the mixed ferrocene-carbonyls. Values of quadrupole splitting span the range... 

The first ferrocene-containing thermotropic liquid crystals, compounds 19 to 21, were reported by Malthete and Billard in 1976. Enantiotropic, 19, or monotropic, 20 and 21, N phases were observed. Compounds 19-21 were designed to undertake Mossbauer studies in mesomorphic media. Ferrocenyl Schiff bases 19-21 represent the first well-characterized organotransition metallomesogens. 

Thiourea forms a layered lattice able to act as host for some organometallic guest molecules. The ferrocene-thiourea inclusion compound has been investigated by spectroscopic methods (NMR, Mossbauer) and it has been shown that the thiourea host structure is preserved [492-502]. Other inclusion compounds of thiourea with organometallics such as ( /" -l,3-cyclohexadiene)Mn(CO)3, (7/ -C6H6)Cr(CO)3, (/ -l,3-cyclohexadiene)Fe(CO)3, and t/ -C(CH2)3Fe(CO)3 have been reported [503, 504]. 

Metallocenes (but only with unsubstituted cyclopentadienyl rings) also form thiourea inclusion compoimds. X-ray diffraction and Mossbauer data on the ferrocene inclusion compound show that at 295 K the guest molecules are orientationally disordered at the sites of 32 symmetry. A phase change at 162 K generates a more ordered structure... 

NMR also has been used to further elucidate the structure and dynamic state of the ferrocene-thiourea inclusion compound [21,22] previously studied by Mossbauer techniques [23], [24] and C [25] NMR. First of all, a new single crystal Mossbauer... 

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