Determination of magnetic susceptibility

Gouy balance A balance for the determination of magnetic susceptibility. The sample is weighed in and out of a magnetic field and the susceptibility is calculated from the difference in weights. 

Fig. 11.54 Schematic diagram of apparatus used for the Faraday determination of magnetic susceptibility. The sample is suspended bdween magnet poles that have been carefully shaped so that the value of HJlSHISx) is constant over the region occupied by the sample.

A recent determination of magnetic susceptibility of PMQ4 by Dr. W. Hatfield (U. of N.C., Chapel Hill) at 10,000 Oersteds showed that susceptibility was independent of temperature from 4 to 300 K. At these high fields, the spins seem to be completely saturated. 

The preparation of many complexes of bipyridyl-containing metals in low oxidation states have been achieved by Herzog and his co-workers (e.g., 367). These and other compounds of interest are cited in Table XVI together with magnetic moments measured at ambient temperature (the most widely determined property). Although most work has been carried out with bipyridyl, it is apparent that phenanthroline and terpyridyl will afford similar complexes. There is a general paucity of physical data for the compounds listed in Table XVI. The determination of magnetic susceptibilities as a function of temperature would be worthwhile in many cases and the two iron compounds are obvious candidates for a Mossbauer study. 

Homer, J., Whitney, P.M. J. Chem. Soc. Chem. Determination of magnetic susceptibilities... 

The standard method for the determination of magnetic susceptibilities of diamagnetic samples is the Faraday-Curie method [8]. The method is based on the measurement of the force on a sample with susceptibility X in an inhomogeneous magnetic field. For diamagnetic substances... 

Other physical methods were also applied to the elucidation of the isomerism of diazocyanides, e. g., determination of diamagnetic susceptibility, the Faraday effect (optical rotation in a magnetic field), and electronic and infrared spectra. Hantzsch and Schulze measured ultraviolet spectra at a remarkably early date (1895 a). Unfortunately, their results and later work (Le Fevre and Wilson, 1949 Freeman and Le Fevre, 1950) did not allow unambiguous conclusions, except perhaps the observation that the molar extinction coefficients of the band at lowest frequency are consistently larger in all types of (i -compounds Ar — N2 - X than in the corresponding (Z)-iso-mers (Zollinger, 1961, p. 62). 

Electrobalances suitable for thermogravimetry are readily adapted for measurements of magnetic susceptibility [333—336] by the Faraday method, with or without variable temperature [337] and data processing facilities [338]. This approach has been particularly valuable in determinations of the changes in oxidation states which occur during the decompositions of iron, cobalt and chromium oxides and hydroxides [339] and during the formation of ferrites [340]. The method requires higher concentrations of ions than those needed in Mossbauer spectroscopy, but the apparatus, techniques and interpretation of observations are often simpler. 

Size of sample 2 was determined using magnetic susceptibility, as described below. 

Spin-state transitions have been studied by the application of numerous physical techniques such as the measurement of magnetic susceptibility, optical and vibrational spectroscopy, the Fe-Mbssbauer effect, EPR, NMR, and EXAFS spectroscopy, the measurement of heat capacity, and others. Most of these studies have been adequately reviewed. The somewhat older surveys [3, 19] cover the complete field of spin-state transitions. Several more recent review articles [20, 21, 22, 23, 24, 25] have been devoted exclusively to spin-state transitions in compounds of iron(II). Two reviews [26, 27] have considered inter alia the available theoretical models of spin-state transitions. Of particular interest is the determination of the X-ray crystal structures of spin transition compounds at two or more temperatures thus approaching the structures of the pure HS and LS electronic isomers. A recent survey [6] concentrates particularly on these studies. 

Ishikawa etal. proposed an approach for the determination of the ligand-field (LF) parameters of a set of isostructural lanthanide complexes. This method consists of a simultaneous fit of the temperature dependence of magnetic susceptibilities and NMR spectra for the whole isostructural series [18]. In order to avoid over-parametrization a key restriction is imposed each parameter is expressed as a linear function of the number of f electrons, n ... 

In many instances several different compositions of the binary oxide and chloride compounds are available. In each case we designate as most common the particular compound that is least expensive and available in the largest quantities from common suppliers,4 as summarized in Table 4.1. Included with each entry is the number (eu) of unpaired electrons determined from magnetic-susceptibility measurements. 

Ring currents cannot be directly determined by experimental methods. However, comparison of experimental values of magnetic susceptibilities and their exaltations and anisotropies as well as of H-NMR chemical shifts with the respective data calculated from the ring current model points to the adequacy of this model for the interpretation of experimental results. The magnetic susceptibility associated with the ring current / (83BCJ1853), known as the London susceptibility, is given by... 

All the same, the quantitative determination of the aromaticity and antiaromaticity from the ring current model may be complicated by at least two problems. First, experimentally observable values of magnetic susceptibilities and their exaltations and anisotropies as well as the H-NMR chemical shifts are not necessarily determined exclusively by ring currents hence, all other effects have to be identified and removed. Naturally, for this model to work, the contribution by the ring current must be predominant. Another problem is that the calculated results on ring current intensities for molecules from the diatropic-paratropic border area may vary qualitatively depending on the method of calculation (80PAC1541). 

Harrison R.J. and Putnis A. (1999) Determination of the mechanism of cation ordering in magnesioferrite (MgFe204) from the time- and temperature-dependence of magnetic susceptibility. Phys. Chem. Miner. 26, 322-332. 

---