Magnetic moment, measurement

Another way in which chemical shifts can be related to absolute shielding is by the comparison of the nuclear magnetic moment (measured by the NMR method for an atom in a molecule) with the moment for the free atom. This has been done with considerable accuracy for hydrogen (SO) and also for lead (50). 

The micelle-encapsulated six coordinated bis(pyridinato) iron(II) complexes of protoporphyrin and OEP have been reported by addition of pyridine to the four coordinate ferrous complex in aqueous micellar solution. The optical spectrum of [Fe(II)(PP)(Py)2] in micelle (Fig. 10) is identical to S = 0 six-coordinate bis(pyridinato) iron(II) porphyrin complex [3]. The magnetic moment measurements in solution confirm their diamagnetic nature. The HNMR spectra are also characteristic low-spin iron(II) resonances (S = 0) with shifts lying in the diamagnetic region (Table 2). 

Magnetic moment measurements suggest that the solids produced in equations (98) and (99) contain Crv and that produced in equation (100) contains CrIv.1370 Other reactions of Cr02F2 are shown in Scheme 123. 

From the magnetic moment measurements shown in Fig. 2(c), a Curie temperature of Tc = 188 K can be derived by linear extrapolation of the inverse magnetic moment to zero. At temperatures slightly below Tc, the magnetic moment stays constant at about 3/4 of its low-temperature value, and the resistivity becomes metallic-like. Moreover, the CJT effect starts to decrease around Tc. As expected for this compound CO sets in at temperatures below TCo = 147 K. This leads to... 

Fig. 6. Field dependence of SQUID magnetic moment measurements around the CJT transition. The solid lines are fits of the data according to equation (1). The absolute values of the magnetization curves at different temperatures are shifted by the indicated offset values for clarity.

Fig. 7. Temperature dependence of the spin-moment 7 around the CJT transition, as derived from the fits of the magnetic moment data with equation (1). The magnetic moment measurements crossing the CJT phase boundary give two corresponding data points, indicated by the solid symbols. The solid line is calculated on the basis of the low-field magnetic moment according to equation (2).

The thermally stable, Schiff base complexes [M(PPD)(C1, ]-j H20 (M = Ir, Pt x = 4 PPD = p-Me2C6H4CH—N(CH2)3NH2) have been prepared characterization by IR spectroscopy shows the dimethylamino and free amino groups to be the coordinating sites. Further characterization by magnetic moment measurements and NMR and electronic spectral data indicates the iridium(IV) complex to be octahedral.568... 

Magnetic moments measured at 25 °C, Mossbauer parameters relative to stainless steel. 

Effective magnetic moment measurements of [Fe(TPP) (CIO ) ] ( ) have yielded values in the range of 4.5-5.3 at 77-300°K. This temperature dependence and range of values is consistent with contributions from sextet and quartet states with the quartet lower in energy. ESR data ( ) for this complex yielded values for g and g of 4.75 and 2.03, respectively. These results are atypical for a high-spin complex and lend further support to the conclusion that the ground state is a S = 3/2 or a 3/2,5/2 mixture with predominant S = 3/2 character. 

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. 

The iron(III) octamethylcorrole 2.136 was later studied in terms of its reactivity towards axial ligands. In this work, Licoccia, et al. determined that, like the ligand-free cobalt(III) corroles, aggregation of the macrocycles occurs in the absence of ligating base. In the presence of pyridine, on the other hand, there is evidence to support the coordination of one axial pyridine ligand. In this instance, the sixth coordination site at iron may be occupied by water. With axially coordinated pyridine, magnetic moment measurements were consistent with the iron center being in a mixed-spin state (5 = 1/2, 5/2). This behavior is similar to that seen for synthetic 5-coordinate iron(III) porphyrins wherein the metal atom is often found to be in a mixed-spin state. ... 

For uranocene the first magnetic moment measurements, due to Karraker, Stone, Jones, and Edelstein (13), date from 1970, and a value of 2.43 B.M., following... 

For the [Anm(Cot)2] anions magnetic moment measurements have been carried out for the Np, Pu, and Am derivatives (63, 64), all in the form of the 2 THF solvates. Thus X-ray diffraction data show that KNp(Cot)2 2 THF and its Pu and Am analogues are all iso-structural, and similar results for the related diglyme solvates indicate that it is extremely probably that these are iso-structural with the salt KCe(Cot)2 diglyme, which is known (23) to have a sandwich structure with D8d symmetry about the Ce atom. Consequently it is reasonable to assume that the pseudo-axial ligand field model is applicable to these [Anin(Cot)2] systems, and to interpret the magnetic data in these terms. 

Ph M (M = As or P) salts of the CrOCl anion have been isolated by reduction of CrOjClj with HCl in acetic acid and precipitation with Ph MCl. Magnetic moments measured were 1.76 and 1.72 BM for M = As and P respectively. The single crystal electronic spectrum of (Ph As)CrOCl4 has been recorded and the bands assigned with the aid of ab initio MO calculations. ... 

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