Effective magnetic moment determination

Figure 10.3a shows the temperature dependence of the effective magnetic moments determined by SQUID for the microcrystalline sample of Fe(OETPP) [34]. The jtiefr values are 3.8-3.9jtiB in a wide temperature range, which are quite close to the spin-only value, 3.87/tiB. expected for the S = 3/2 state. Figure 10.3b shows the Mossbauer spectrum of the same complex taken at 77 K for the microcrystalline sample. The IS and QS values are 0.42 and 3.02 mms , respectively. The large QS value supports that the complex adopts the intermediate-spin state [38-40]. 

Useful applications of the Evans proton NMR shift method have permitted the determination of effective magnetic moments peff (see Section 8) and spin multiplicities for several high-spin radical-cation species.This work makes available a simple procedure for such assignments when the spin carriers are stable in solution. 

The number of unpaired spins for an ion in its ground state is obviously determined by the multiplicity, 2 -fl, of that state and vice versa. The multiplicity is written in the upper left hand comer of the symbol for the state. Thus the ground state symbol can be read off from the appropriate correlation diagram and, if spin-only conditions apply, the effective magnetic moment can be immediately determined. 

When ethylenediamme is. aided to a solution ofcobaltfll) chloride hexahydraic in concentrated hydrochloric acid, a Hue crystalline solid is obtained in 80% yield. Analysis of this compound shows ihal it contains 14.16% N. 12.13% C. 5.09% H. and 53.70% Cl. The effective magnetic moment is measured as 4.6 BM. The blue complex dissolves in water to give a pink solution, the conductivity of which is 852 ohm 1 cm mot"1 at 25 °C. The visible spectrum of a dmso solution of the complex his bands centered at 3217.5610. and 15,150 cm" (molar absorptivity = 590 mol-1 Lem-1), but for a water solution, the absorptions occur et 8000. —16.00031x119.400cm-I(nx)lar absorptivity = 5 mol-1 Lem-1). In u titration with sodium hydroxide, each mole of Ihe complex neutralizes four moles of base. Determine the formula and structure of the complex. Account for dll reactions and observations. 

Using the compositional dependencies of the magnetic moment and the effective magnetic moment of the alloys (Fig. 5), we can determine the magnetic moments and the effective magnetic moments of Mn and Ni atoms (see Table 2) from the formulae... 

Besides the oxide Cr02 and the chromates(IV) (see Section 3.3), there exists a number of Cr alkoxides [Cr(OR)4] derived from tertiary alcohols. These are volatile blue liquids or low-melting sohds with effective magnetic moments of ca. 2.8/tb The crystal structure of [Cr OCH(r-Bu)2 4] has been determined and confirms the tetrahedral coordination geometry of chromium. The short Cr distances (177.3 pm) indicate significant ligand metal 7T-donation. 

Orbital contributions in general determine departures of the g value from the free electron value, and introduce magnetic anisotropy. Equation (1) shows that the quantity XmT is independent of temperature. Sometimes instead of Xm a dimensionless quantity, the so-called effective magnetic moment /iefr=2.828 (xm7) is used, but in the recent literature the XmT value is usually reported. The spin-only XmT and //eff values for various numbers of unpaired electrons are given in Table 1. It is much more common for the magnetic susceptibility to use cgs rather than SI units and we will use the former throughout this chapter. 

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