Periodic table, Mossbauer

Fig. 1.1 Periodic table of the elements those in which the Mossbauer effect has been observed are marked appropriately. (Taken from the 1974 issue of [10])...

Kaindl et al. [186] have plotted the isomer shift results for metallic hosts versus the number of outer electrons of the 3d, Ad, and 5d metals and found the transition energy to decrease when proceeding from a to a Ad and further to a 3d host metal in the same column of the periodic table. This systematic behavior is similar to that observed for isomer shifts of y-rays of Fe(14.4 keV) [193], Ru(90 keV), Pm (77 keV), and lr(73 keV) [194]. The changes of A(r ) = (r )e — (r )g for these Mossbauer isotopes are all reasonably well established. Kaindl et al. [186] have used these numbers to estimate, with certain assumptions, the A(r ) value for Ta (6.2 keV) and found a mean value of A(r ) = —5 10 fin with some 50% as an upper limit of error. The negative sign of A(r ) is in agreement with the observed variation of the isomer shift of LiTaOs, NaTaOs, and KTaOs, as well as with the isomer shift found for TaC [186]. 

Table I shows the various Mossbauer nuclides—i.e., the nuclides where the Mossbauer eflFect has actually been seen. Not all of these are as easy to exploit as the Fe and 9Sn cases referred to above. However, with improved techniques a number of these should prove accessible to the chemist. Representative elements of almost all parts of the periodic table are tractable by these techniques. It seems clear, however, that the methods of Mossbauer spectroscopy are no longer technique-oriented but that this field is becoming a problem-oriented discipline. In other words, the Mossbauer effect is now used successfully in many cases not only to demonstrate the effect or to corroborate physical evidence obtained by other means—NMR, or infrared, or kinetic studies— but also to solve new chemical problems.

Dr. Erickson For those interested in coordination chemistry, certain other transition metal atoms are suitable for Mossbauer spectroscopy. One in particular is ruthenium which is just below iron in the Periodic Table. It is a difficult isotope to work with since it requires helium temperatures almost exclusively. I don t know whether it is possible to work at nitrogen temperatures or not, but Kistner at Brookhaven has examined various ruthenium compounds from the 2-j- to the 8+ oxidation states with interesting results. These are not published yet, but at least his work offers the possibility of going down one element below the other in the Periodic Table to study chemical effects. Osmium, which is below ruthenium, can also be Mossbauered. Some sort of systematic study like this involving elements in the various transition series would be extremely interesting. 

Figiire 2. Periodic table. Shaded, essential elements small dots, may be observed in Mossbauer absorption mode and large dots, may be observed in Mossbauer emission mode. 

Selected properties of the element are shown in Table 1.1.1. It is in Group 14 of the Periodic Table, with the electronic configuration [Kr] 4d ° 5s 5p its principal valence state is Sn(IV), though Sn(II) inorganic compounds are common, and many stannous organic compounds, with specially designed structures, have been prepared in recent years. Tin has 10 stable isotopes (Table 1.1.2), which is the largest number for any element, and results in very characteristic mass spectra. The " Sn and Sn isotopes, each with spin 1/2, are used in NMR spectroscopy. The y-active " Sn isotope, which is prepared by the neutron-irradiation of enriched Sn, is used in Mossbauer spectroscopy. 

The chemical bonding in iodine compounds is much simpler to describe than that in tin, antimony, or tellurium which precede it in the Periodic Table. This is particularly true where the iodine forms only one bond to another atom. As a result it is possible to develop a quantitative interpretation of the Mossbauer parameters. The equations given here were first formulated by Hafemeister et al. [74] and subsequently revised to a more elegant form by Perlow and Perlow [72]. 

Fig. 3. Periodic table of Mossbauer transitions abreviations RG - rare gases Ln lanthanides and Ac - actinides...

Figure 3 presents the periodic table of the Mbssbauer transitions showing the number of the isotopes in which the Mossbauer eflFect has been observed (lower left corner) and number of the nuclear transitions (upper right corner) for each element exhibiting a Mossbauer effect. In respect of the basic concepts of the structural inorganic chemistry [19, 20] the elements are grouped into three main groups as follows i) elements without a Mossbauer isotope ii) elements with an uncommon Mossbauer isotope and iii) elements with a common Mossbauer isotope. 

On the other hand, it is well known that not all chemical elements possess Mossbauer isotopes. This is an important limitation in the lithium battery field, as common electrode materials in commercial products contain Li, Co, C, O, or P, which have no Mossbauer nuclei. Fortunately, other valuable elements in the electrodes of commercial Li-ion batteries can be studied by this technique. Thus, Fe- and Sn-containing active electrode materials and the less commonly studied Ni have been the basis of thorough investigations. Moreover, many other elements, although not always involved in commercial Li-ion products, have been extensively investigated in lithium test cells and possess Mossbauer isotopes. Among these, Zn, Ge, Ru, Ag, Sb, Te, and iodine can be highlighted. This information is summarized in the form of a periodic table In Fig. 28.2. 

Fig. 1.1. A periodic table of elements with Mossbauer isotopes. The elements with easier to use and more extensively studied isotopes are shown shaded, while those with more difficult to use and less extensively studied isotopes are shown hatched. These two categories were distinguished by whether more or less than one hundred papers were published on work with these Mdssbauer isotopes between 1953 and 1982 (Long, 1984). It should be noted that in this period 10000 papers were published on studies involving the most extensively used isotope Fe.

The most prominent nuclide for Mossbauer speetroseopy is Fe, with over 90% of the 50000 or so publications that make use of this technique referring to this isotope. Reports range from compound identification in complex chemistry, through the bioinorganie chemistry of iron, to industrial studies of corrosion of metals and even water detection on Mars (in water-containing iron minerals [1,2]). However, the Mossbauer Effect is applicable to more than forty elements, as indicated in the Periodic Table inside the front cover. 

Figure 5.13 Elements in the periodic table with Mossbauer isotopes (in bold font).

If a diffusional model with AHm < kT is appropriate, then the time th between electron hops must approach the period cor of the optical mode vibrations that trap or correlate the electrons. With an wj = 10" s, the hopping time Th would be short relative to the time scale of Mossbauer spectroscopy, ca. 10" s. We can therefore anticipate an isomer shift for the octahedral-site iron that is midway between the values typical for Fe ions and Fe " " ions. From Table 1 and Eq. (1), we can predict a room-temperature isomer shift of 6 0.75 mm/s wrt iron. Consistent with this prediction is the... 

TABLE 13.1 Mossbauer Parameters for Fe(lll)-Containing Aqueous Solutions of 5-Methylresorcinol and 4-n-Flexylresorcinol (Containing 20% (v/v) Ethanoi see aiso Fig. 13.2) at pFI 3 (Total [Fe] = 16 1 mM 1 3 Fe-to-AlkyIresorcinol Molar Ratios), Rapidly Frozen After Specified Periods of Time, and for Their Solid Residues Obtained by Drying in Air at Ambient Temperature (Measured at 7= 80 K) [53] ... 

In the soil diazotrophic rhizobacterium A. brasilense (strain Sp245, reported to be tolerant to submillimolar concentrations of heavy metals, including cobalt(ll), in the culture medium [32]), EMS studies were first performed on freeze-dried bacterial samples (measured at T = 80K Fig. 17.2) [27]. The following experiments with the same bacteria were performed with live cells rapidly frozen after certain periods of time (2-60 min) of contact with Co", and EMS spectra were measured for frozen suspensions (without drying), which more closely represent the state of cobalt in the live cells [31,32] (Fig. 17.3). Mossbauer parameters calculated from the experimental data are listed in Table 17.1. 

In Fig. 17.4, the Mossbauer parameters are plotted for different cobalt(ll) forms in each sample and for various periods of contact (2 and 60 min) of the live bacteria with Co", as well as for dead bacterial cells (thermally killed by storing in the medium at 95 °C in a water bath) and for the cell-free supernatant liquid [5,31]. The EMS data for different periods (2 min and I h) of contact of live bacteria with Co + traces essentially differed in the corresponding QS values (see Table 17.1) for the two (+2) forms [31 ]. This finding indicated that within an hour, after primary rapid adsorption onto the cell surface, cobalt(ll) underwent further transformation, most probably occurring within the cell membrane. Nevertheless, the parameters for live bacteria after 2 min and for dead bacteria were found to be rather close (essentially... 

TABLE 17.1 Mossbauer Parameters Calculated from Emission Mossbauer Spectroscopic Data for Aqueous Suspensions of Live and Dead Cells of Azospirillumbrasilense Sp245 in the Co"-Containing Culture Medium as well as for the Cell-Free Supernatant Liquid, which were Incubated with CoCl2 for Specified Periods of Time at Ambient Temperature and then Rapidly Frozen in Liquid Nitrogen (Spectra Measured at 7= 80 lO [27,31,32]) ... 

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