Magnetic susceptibility average

Contents 1. Introduction 160 2. Methods to Achieve High-Resolution NMR Spectra in the Presence of Delaying Media 161 2.1. MAS for magnetic susceptibility averaging 161 2.2. Chrom-NMR without MAS 162 3. Mobility PFG 162 3.1. Diffusion NMR and its representation 162 3.2. Diffusion in multiphasic environments 164 3.3. Specificity of diffusion PFG measurements in porous media 165 4. Examples of Chrom-NMR 166 4.1. Comparison with Liquid Chromatography (LC) 166 4.2. Non-chromatographic mobile phases 169 5. Conclusions 171 Acknowledgements 172 References 172... 

The magnetic exaltation E is the difference in the average magnetic susceptibility (averaged over all orientations of the molecule with respect to the applied magnetic field) and empirically estimated susceptibility [3]. The latter is calculated as the sum of the atomic susceptibilities and an increment due to the presence of double bonds [4,5] = EaXa + where n is the number of double bonds). Systems... 

Fig. 1. Orientationally averaged magnetic susceptibility of various forms of carbon [21].

Following the completion of the sintering study, a study was conducted to demonstrate that 663 K, the temperature at which all magnetic susceptibility measurements were taken, was indeed greater than Tq, . As discussed in the theory section, measurements were made at several temperatures until it was determined that plots of M/Mg versus H/T collapsed onto a single curve. It is clear from Figure 4 that Tqj, must be less than 450 K. That is, for any temperature above 450 K the average particle size was measured to be nearly 200 A in diameter. For smaller particles, Tq, will of course be an even lower temperature. This proves that all measurements made at 663 K were indeed accurate. 

Fe(isoxazole)6]2+ and [Fe(isoxazole)4(H20)2]2+, together with four non-co-ordinated tetrafluoroborate anions (Fig. 15). The structural details for the low-field trans [Fe(isoxazole)4(H20)2]2+ are consistent with a high-spin Fe(II) chromophore (average Fe-O=2.09 A and Fe-N=2.19 A), whereas those for [Fe(isoxazole)6]2+ show a marked temperature dependence (average Fe-N=1.98 A at 115 K and 2.17 A at 231 K) related to the reversible low-spin to high-spin transition. From magnetic susceptibility measurements, the transition temperature has been found to be T1/2=137 K. 

However, the replacement of two bpym molecules by weaker ligands such as pyridine (py) and particularly NCS affords the compound [Fe(bpym) (py)2(NCS)2]l/4py (Fig. 2). The average Fe-N bond length, 2.186(8) A, at room temperature, is consistent with an iron(II) ion in the HS state. The thermal dependence of XmT (XM=molar magnetic susceptibility, T=tempera-... 

Although the interpretation of this effect is not entirely straightforward, it most likely reflects an increase in magnetic susceptibility on going from the pol3mier to the mononuclear dicitrate chelate. In addition, the interaction of the irons with the solvent water is no doubt increased on the average as the polymer is dissociated. 

The nc value for palladium-hydrogen is 0.25 from magnetic susceptibility measurements (52) with Tc = 564°K (52), and from P-C-T data, de Ribaupierre and Manchester (26) estimate nc = 0.29 and Tc = 566°K. The Bragg-Williams approximation gives a reasonable WfiH value by using an average value of nc, the critical temperature, and an analytical expression for ie(n) determined... 

The molecular magnetic susceptibility anisotropies for the pyranones have been determined by microwave techniques (71JA5591, 73JA2766). Values for the parameter A, which represents the out-of-plane minus the average in-plane molecular magnetic susceptibilities, were obtained for benzene, furan, 2- and 4-pyranone, and tropone. A may be separated into local and non-local contributions with the aid of known local group contributions for non-aromatic molecules. The results are presented in Table 12. 

Ginsberg et al.2917 made a detailed analysis of the average magnetic susceptibility of nickel(II) dimers and fitted the temperature dependence of the magnetic susceptibility of [Ni2(en)4X2]Y2 (X, Y = Cl, Br X = NCS, Y = I). The model Hamiltonian they used is... 

In suitable systems the g-value can be measured with great accuracy. Also, the ESR experiment is such that each paramagnetic ion contributes separately to the spectrum, and in principle the contributions can be obtained separately. This is in contrast to the magnetic susceptibility, where the experiment reflects only the average of the contributions of individual ions in a crystal. 

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