Magnetic properties high-spin complexes

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. 

The observed properties of MMB are also best understood in the light of our calculated sextet ground state and close lying quartet state. For example, magnetic susceptibility measurements ( ) of MMB indicate that it is primarily a high-spin complex at low temperature (27) but that decreases from pure high-spin values as the temperature increases. Mdssbauer spectra ( 12) of MMB gave a value of AEq = 1.33 mm/sec. This value also appears to reflect a contribution... 

High-spin and low-spin states are readily distinguished by the magnetic properties of a complex. Since the environment of the central atom is not spherically symmetrical, the orbital angular momentum is not conserved and makes no contribution to magnetic behavior. The orbital angular momentum is said to be quenched by the crystal field. 

Magnetic properties o( s< Central No. of d metal electrons )me complexes of the first-row transition metals" High spin complexes Low spin complexes ... 

In practice, electrons prefer to occupy an unoccupied orbital first, before sharing an orbital with another electron. If they do share an orbital, then they must do so with an opposite spin. If there s a case where there are lots of unshared electrons, the complex is said to be a high spin complex, but if the electrons are all paired together, then it s called a low spin complex. This affects the magnetic properties of the complex. 

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