Magnetic properties, from crystal field

Magnetic Properties from Crystal Field Theory... 

Among the early successes of crystal field theory was its ability to account for magnetic and spectral properties of complexes. In addition, it provided a basis for understanding and predicting a number of their structural and thermodynamic properties. Several such properties are described in this section from the crystal field point of view. Certainly other bonding models, such as molecular orbital theory, can also be used to interpret these observations. Even when they are, however, concepts from crystal field theory, such as crystal (or ligand) field stabilization energy, are often invoked within the discussion. 

The values of A have been tabulated. In the cases of Eu " and Sm ", there are substantial magnetic contributions from excited states. Eu " with a ground state of Fo, which is diamagnetic, depends totally upon the Fi,2.3 excited states, which are thermally accessible, for its magnetic properties. From the equation it follows that for one complex of any individual lanthanide, the relative dipolar shifts of all the nuclei are determined by their geometric relationship in terms of d,

isostructural series of complexes of different lanthanides, the shifts of analogous nuclei are related only by the values of A, assuming the crystal field parameters are not appreciably different. 

Calculation of single-center magnetic properties from the ligand-field eigenvectors requires input of Stevens orbital reduction factor, k, and the temperature. CAMMAG provides the principal molecular and crystal susceptibilities and g-values (for odd-electron systems) and their orientations. 

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. 

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