Jahn-Teller distortion, spin-orbit quenching

Interestingly, aU cyanide SMMs reported thus far are characterized by the presence of ions with appreciable spin-orbit coupling. In the prototypical Mnj2 SMMs, the orbital angular momenta of Mn(III) centers are quenched due to the tetragonal Jahn-Teller distortion. This is not the case for the compounds listed in Table XI. In the molecules based solely on 3d transition metals, important orbital contribution results from the presence of low-spin Fe(III) centers. The only exception is the pentanuclear TBP cluster [Mn (tmphen)2l3[Mn (CN)6]2 (177). This compound was subjected to a detailed theoretical treatment that... 

The orbital angular momentum is reduced from what it would be in the free metal ion by the presence of ligands. The orbital contribution to the magnetic moment is said to be quenched if the symmetry of the complex is lowered as in Jahn-Teller distortion. Thus the value of magnetic moment approaches the spin only value... 

All the off-diagonal matrix elements of the spin-orbit coupling in the >, Tl> [ basis are thus reduced by the factor y, and we use the experimentally observed quenching to calculate Ej j and the corresponding geometrical distortion (14). In the Cs2NaYClg host lattice the total spread of the four spin-orbit components of T2 is 32 cm whereas crystal field theory without considering a Jahn-Teller effect predicts a total spread of approximately 107 cm-. ... 

Moreover, the state is in principle Jahn-Teller unstable, and any such distortion can lead to partial quenching of spin-orbit splittings [28]. 

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