Paramagnetic fractions

Fig. 28. Normalized (to T = 250 K) (iSR signal amplitude (= paramagnetic fraction) from TF measurements on polycrystalline YMh2. After Weber et al. (1994a).

Fig. 68. [xSR spectra of Y(,Tb(i, Mn2 at 90 K (warming) taken in TF=100G, ZF and LF=20G and 200 G (from bottom to top). These four spectra were least squares fitted simultaneously. The inset shows the temperature variation of the paramagnetic fraction (compare with the data for pure YMnj in fig. 28). After Kalvius (1994). 

Fig. 121. Top ZF-M.SR spectrum of CcAlj at lOmK. The broken lines show the decomposition of the fit (solid line) to the spectrum into 3 subspectra (the Bessel-damped oscillatory pattern and the exponentially damped 1/3 signal from the magnetic finction together with the weakly Gaussian-damped spectrum of the paramagnetic fraction). Bottom Temperature dependence of the maximum fi equency in the oscillatory signal of CeAlj (open circles, left-hand scale) and of the magnetic volume fraction (sohd circles, right-hand scale). The lines are guides to the eye. Aflcr Amato (1997).

Paramagnetic fractions produce quadrupole doublets (QS) in the spectrum. Their parameters are close to those of hydroxides (e.g., lepidocrocite, y-FeOOH) or to small superparamagnetic particles of iron oxides or hydroxides with a mean diameter of about 10 nm. It should be noted that it is not difficult to distinguish among different magnetically ordered phases when they are present in a well-ordered crys-... 

The only example of xenon in a fractional oxidation state, +, is the bright emerald green paramagnetic dixenon cation, Xe [12185-20-5]. Mixtures of xenon and fluorine gases react spontaneously with tiquid antimony pentafluoride in the dark to form solutions of XeF+ Sb2 F, in which Xe is formed as an iatermediate product that is subsequently oxidized by fluorine to the XeF+ cation (83). Spectroscopic studies have shown that xenon is oxidized at room temperature by solutions of XeF+ ia SbF solvent to give the XE cation (84). 

K did not produce tiny new paramagnetic species, despite FTIR observations confirming appearance of IR features attributable to adsorbed NjO (2234 and 1256 cm in Fig. 4a) upon contact with N2O at 300 K. Stepwise decreases in magnitude of those IR features were, however, observed in each of a sequence of FTIR spectra taken after separate NjO adsorptions at increasing adsorption temperatures (TJ up to 573 K (Fig. 4b-d). From these FTIR observations it could be inferred that increased T, for contact between N,0 and vacuum-outgassed CeOj resulted in increased fractional decomposition of the N O introduced. FTIR spectra did not show bands due to peroxide species after N,0 adsorption. 

It should also be stressed here that many of these complexes are neutral and therefore relatively soluble in common organic solvents, an important issue for their purification and crystallization. Among all these paramagnetic complexes, only a fraction has been investigated for their magnetic properties in the solid state,... 

Figure 2 Correlation diagram for H NMR spectra of Cp Fe(Et2C2B3H3)CoCp in CDCI3 (for the oxidation) and THF-ds (for the reductions), showing <5 plotted vs. mole fraction of the paramagnetic component (g.70 Reproduced with permission of the American Chemical Society.

NMR has also been used to characterize binding [22, 23]. When cyt c binds to ccp the paramagnetically shifted heme methyl groups of cyt c shift further downfield by 1-2 ppm. Normally, binding occurs in the fast exchange regime, so that the fraction bound can be assessed from the frequency shift (Fig. 10). Two... 

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