Magnetic moments, effective

We can define an effective dipole moment as /tM = A BPeff where Peff is experimentally determined. For the rare earth ions, peff = gs/ViV +1)/ where / is calculated from the Hund s rules as outlined above. However, for the transition elements, Peff = gy/S S + 1) where the orbital component apparently makes no contribution. Here we say the orbital angular momentum is quenched. For the transition elements, the d-electrons lie close to the outer regions of the atom and are acted upon by neighboring crystal fields that perturb the orbits so as to eliminate its contribution to the magnetic moment. The/-electrons in the 

---

The g-factors of radicals 101 and 102 are 2.0065 and 2.0059, respectively. The pyrazolylnitroxides have effective magnetic moments at room temperature corresponding to the standard values for one unpaired electron per molecule (1.71 0.05 B.M.). The values of effective magnetic moments of the nitroxyls practically do not change in the temperature range 5-300K. 

Consider the orbital angular momentum of a free-ion term. Here L = 3 and the orbital degeneracy is 7. Application of Van Vleck s formula (5.8) predicts an effective magnetic moment. 

Figure 10-3. Comparisons between typical observed effective magnetic moments ( ) and those calculated (---) with Eq. (10.1).

Fig. 1. Plot of effective magnetic moment vs. iron-sulfur bond length in [FeCRidtcls] complexes.

Figure 2. Plot of relative magnetization, a/Os ns a function of H/T. (a) A paramagnetic system Is characterized by an effective magnetic moment, with a Bohr Magneton number vlO per Ion, and by the absence of hysteresis. Paramagnetic saturation occurs at very high "H/T" == 10 Oe K"l. (b) l.angevln curve for S.P. clusters, (c) Part of a ferromagnetic hysteresis curve.

Fig. 1 The temperature dependence of the effective magnetic moment of [Fe(HB(pz)3)2] during heating and cooling. Data obtained from Fig. 3 of [30]... 

The inverse magnetic susceptibility and the effective magnetic moment, jueff, of [Fe(HC(3,5-(CH3)2pz)3)2](BF4)2 are shown in Fig. 16 where it is immediately obvious that the magnetic properties of this complex are quite unusual [46]. Above ca. 210 K the eff of ca. 5.0 is clearly that expected of a high-spin iron(II) complex. But below ca. 190 K the moment decreases to a substantially lower value of ca. 3.7 /uB. Further, at ca. 90 K there is a small irreversible change in susceptibility and moment, a change that is associated with crystal reorientation in the applied field. The reason for the abrupt decrease in the moment at ca. 200 K to ca. 3.7 becomes apparent from a study of the Mossbauer spectra of [Fe(HC(3,5-(CH3)2pz)3)2](BF4)2. 

Fig. 16 The temperature dependence of the inverse molar magnetic susceptibility, a, and the corresponding effective magnetic moment, b, of [Fe(HC(3,5-(CH3)2pz)3)2](BF4)2. Data obtained from [46]...

The analysis of the magnetic and structural data reported by Ryabova revealed a linear correlation between the Fe-S bond distance and the effective magnetic moment [106]. 

An additional, independent estimate of the concentration of paramagnetic superoxo and diamagnetic hydroperoxo-/peroxo-titanium species was made from magnetic susceptibility measurements using a Lewis coil force magnetometer (52). The gram-susceptibility of Ti in TS-1 + H2C>2 was estimated to be 5.5 X 10-6 emu/g, which corresponds to an effective magnetic moment of... 

B.M. If all the Ti ions in the sample had formed superoxo species upon interaction with H2O2, the effective magnetic moment should have been 1.73-1.78 B.M. The concentration of superoxo-Ti species is, thus, about 45% of the total Ti, comparable to the values found by EPR (55%) and electronic spectroscopies. The remaining fraction is, presumably, the diamagnetic hydroperoxo-/peroxo-Ti species. 

Magnetic Susceptibility and EPR Data. The temperature dependent magnetic susceptibility and EPR of the S -ethylporphyrazines were measured and the effective magnetic moments ([teff), spin, and J values are reported in Table XIV (113, 116). 

The effective magnetic moment of the monoanion [NiL2]- (/reff = 2.14 pB in the solid state, at 300 K) supports the Ni(III) attribution. In addition... 

---