Susceptibility, molar paramagnetic

Fig. 4. Curves showing the reciprocal of the molar paramagnetic susceptibility of Ni, Pd, and Pt as a function of the temperature.

Fig. X-2.—Curves showing the reciprocal of molar paramagnetic susceptibility of nickel, palladium, and platinum as a function of the absolute temperature.

Figure 3.14 Plot of molar paramagnetic susceptibilities, yM, as a function of pH forO.Ol M Fe (I I l)TM PyP (solid circles) and 0.01 M Fe(II l)TPPS4 (open circles) aqueous solutions. Actual compositions can be found in the original literature. Insert schematic representation of a dimeric Fe g-oxo porphyrin (see also G in Scheme 3.2).

Only the c(0), c(l) and c(2) coefficients enter the van Vleck formula for the components of the molar paramagnetic susceptibility which relaxes to the polynomial fit formula of the form [5]... 

The temperature dependence of the molar magnetic susceptibility (x) of an assembly of paramagnetic spins without interaction is characterized by the Curie behavior with x = C/T where C = /Vy2( 2.S (.S + l)/3k. It is a very common situation in the organometallic chemistry of radical species when the spin density is essentially localized on the metal atom. Since, in most cases, this atom is surrounded by various innocent ligands, intermolecular interactions are very weak and in most cases are reflected by a small contribution described by a Curie-Weiss behavior, with x = C/(T 0) where 0 is the Curie-Weiss temperature. A positive value for 0 reflects ferromagnetic interactions while a negative value — the most common situation — reflects an antiferromagnetic interaction. 

The paramagnetic susceptibility of pure FeAl204 (x = 2) gives a Weiss constant 0 = -144 K and a molar Curie constant (emu) = 3.80 K, somewhat large for high-spin Foa ions with a spin-only moment however, there is no apparent antiferromagnetic ordering of the FeA -ion spins down to 9.5 K, where a peak in the susceptibility has been associated with a local Jahn-Teller distortion about the Fe ions ... 

The PVP-Cr(III) complex is paramagnetic because a Cr(IlI) ion possesses three spins (3d3). The molar magnetic susceptibility of the FVP-Cr(IH) complexes given in Table 3 is the same as that of the pyridine-Cr(III) complex. The ESR spectra of PVP-Cr(III) are similar to that of pyridine-Cr(III). Thus, we considered that the Cr(III) complexes on the FVP chain were magnetically dilute and the Cr(III) ions did not interact with each other, although they coordinated along the PVP chain at high concentration. 

Transition-metal (dn) complexes with open shells belong to the class of paramagnetic materials their magnetic susceptibility is positive (the sample is attracted to the magnetic field) and is temperature dependent. At high enough temperatures and in small fields, the molar magnetic susceptibility normally obeys the Curie law... 

Example 6. For paramagnetic materials the magnetic susceptibility may be measured experimentally and used to give information on the molecular magnetic dipole moment, and hence on the electronic structure of the molecules in the material. The paramagnetic contribution to the molar magnetic susceptibility of a material, xm, is related to the molecular magnetic dipole moment m by the Curie relation... 

For these physical properties only theoretical results from a simple ab initio FSGO calculation are available. The average polarizability a = 4.107 and the molar, dia-, and paramagnetic susceptibilities (in 10" emu/mol) Xm = 16.430, %d = 21.482, %p = 5.053 were obtained. 

Fig. 1. Composition dependence of the experimental molar magnetic susceptibility Xexp and its components, the paramagnetic Xp and diamagnetic Xd susceptibilities, of semiconducting glasses of the system As-Se synthesized at the maximum temperatures a) 750 C (conditions I) b) 900 C (conditions II).

The first information which is possible to obtain from the measurement of the paramagnetic susceptibility of the compounds is the number of unpaired electrons per metal ion, n. In fact in the spin-only limit, and assuming that no interaction between the magnetic centers occurs, the molar magnetic susceptibity Xm is given by the Curie law ... 

It is often found that the Curie law Eq. (21) is followed by many magnetically dilute substances other than free atoms or ions. There is, in addition, a second-order contribution to the paramagnetic susceptibility, the so-called temperature-independent paramagnetism Not. (also abbreviated TIP, cf. section 1,1.3.6) which arises from states separated from the ground state by an energy k T It follows that the molar susceptibility corrected for diamagnetism may be frequently represented by the Langevin-Debye expression... 

Fig. 158. FeCl2 2H20. Temperature dependence of reciprocal molar magnetic susceptibilities in the paramagnetic region. (pJ.,=4.65mb. (0p)..,=5K ...

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