Mossbauer parameters polymers

The similarity between the Mossbauer parameters of ferritin and a synthetic polymer derived from hydrolysed ferric nitrate have been pointed out previously (101) the polymer has a similar room temperature Mossbauer spectrum with isomer shift and quadropole splitting of 0.48 and 0.67 mm/sec. respectively. At very low temperatures the spectrum of the polymer is also closely similar to ferritin. 

Linear, saturated, polymers obtained by radical initiation of 1,1 -divinylferrocene hive the Mossbauer parameters (6, 0.23 mm s l LEq, 2.29 mm s l) expected for cyclopolymer8 with three-carbon bridged ferrocene units in the main chain. However, cationic initiation yields polymers which exhibit differences from the radical polymers in Mossbauer (, 0.27 mm s 7 Eq, 2.40 ntn s 7) and other spectroscopic studies. The cationic polymers may contain a bicyclic unit or a ladder structure in the chain. 

These results therefore indicate that the soluble, saturated polymers produced by radical initiation of DVF are cyclopolymers containing a three-carbon bridged ferrocene unit (I). However, the Mossbauer spectra obtained for polymers produced by cationic initiation do not show evidence for the three-membered bridge. Certainly PDVF(cationic) contains some acyclic unsaturated units, not necessarily pendant vinyl groups (II), but the low level of unsaturation suggests that cyclic units exist. Thus, for example, a five-carbon bridged bicyclic unit (VI) or a ladder structure (VII) may be found in these polymers, and would be consistent with the Mossbauer parameters obtained. Further polymerisation studies and Mossbauer and other spectroscopic studies of these polymers are in progress. 

Table 4.3. Mossbauer parameters of FeCl4 anion in different conjugated polymer matrices.

The Mossbauer parameters of iron(III) chloride dissolved in benzene (<5 = 0, =0.36) are almost the same as those of anhydrous iron(III) chloride measured in the solid state. This shows that the interaction between the benzene molecule and the iron atom is very weak the charge symmetry and the s-electron density on the iron nucleus do not change in the course of dissolution. Accordingly, in an iron(III) chloride solution in benzene dimers or polymers are to be present which are unsolvated or solvated to only an extremely small extent. 

The analysis of the Mbssbauer spectra of the three diorganotin(IV) ciprofloxacinate complexes allowed the calculation of the Mossbauer parameters, isomer shifts, 8, and quadrupole splittings, lA I, reported in Table 12.5. Each complex showed the occurrence of a characteristic two doublets spectrum. This indicates that two different tin(fV) environments exist in the organotin polymers. The values of Mossbauer... 

A satisfactory statistical fit to the data could be obtained, however, with three symmetric doublets, which were attributed to central, peripheral, and oxidized iron sites in the polymer. The associated Mossbauer parameters are listed in Table X. 

Other physical parameters of the micelle also suggest that the cores of ferritin and ferric nitrate polymer are closely related. The magnetic susceptibility of the iron micelle is 3.84 Bohr magnetons. The Mossbauer spectrum for ferritin observed by Boas and Window (39) and by Blaise et al. 40) are in close agreement with the spectrum for the ferric nitrate polymer as well as the ferric citrate and ferric fructose polymers. Most interesting is the fact that the size of the ferric hydroxide polymer in the ferritin molecule is practically identical to that observed for the ferric nitrate and ferric citrate spheres. 

There have been Mossbauer studies of Nafion membranes by several groups (J —6), besides some work on other ionomers (7,8) and a body of results on polymers where iron or tin is introduced into the polymeric matrix as a probe impurity (8). This chapter will concentrate on the information that has been extracted from the Mossbauer studies of Nafion membranes, and their variations as a function of parameters such as temperature, applied magnetic field, water content and chemical treatment. The results will be discussed in terms of the information they provide about the structure of the ionic phase in perfluorosulfonate materials. 

Mossbauer spectroscopy is a rather exotic characterization method in polymer chemistry. We will therefore briefly outline the principles of this method with special emphasis on three principal parameters describing the Mossbauer spectrum. 

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