Basic Mdssbauer spectroscopy

Soluble pigments The most important pigments in this class are the metallic chromates, which range in solubilities from 17 0 to 0-00005 g/1 CrO . An examination has recently been carried out of the mechanism of inhibition by chromate ions and it has been shown by chemical analysis of the stripped film, Mdssbauer spectroscopy and electron microprobe analysis that the air-formed film is reinforced with a more protective material in the form of a chromium-containing spinel (Chapter 17). The situation is, however, complicated by the possibility that some chromates, particularly the basic ones, may inhibit through the formation of soaps. There is evidence that lead chromate can function in this way. 

The nature of acid sites was at the center of several studies. Barthomeuf discussed spectroscopic methods applied to study hydroxyl groups, Bronsted and Lewis acidities and basicities, and the effects of extraframework oxides on acidity or basicity. These are IR, which is the most important here, NMR, XPS, UV- and visible, Raman and Mdssbauer spectroscopies. Far infrared technique may reveal cation locations. The shift of the band associated with the NH of pyrrole depends on the charge of 0, which in turn determines the basicity. Some progress has been made in the last few years in the identification of different OH groups. An interesting observation was that sU adsorbed benzene molecules are disturbed by the 0-s, even at high benzene coverages. 

For the sake of completeness and in order to help the uninitiated reader to understand the termini technici we start out with a short summary of the essential physical background of Mdssbauer spectroscopy and of the physical nature of the parameters to be extracted from a Mdssbauer spectrum (section 2). A brief overview of the basics of the technique particularly with respect to measurements on Np and high-pressure experiments as carried out by our group follows in section 3. 

Very weakly basic anions like the sulfonates (803 " and S03CF3 ) and the fluoroantimonates (SbF ", Sb2Fn , or Sb3Fig ) allow the stabilisation and study of highly electrophilic cations, both in the respective acid or superacid solutions or in solid, thermally stable compounds. The examples discussed here include main-group cations like a) (CH3)2Sn2+, which is studied by 1 l Sn Mdssbauer spectroscopy and allows the estimation of anion nucleophilicity or b) the molecular cations 02", Br2 , and l2" studied by magnetochemical techniques. 

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