Low versus High Spin States

Fig. 2.2 Calculated values for the high to low spin state transition energy for supported transitions metal atoms on the regular MgO(OOl) surface versus the corresponding values for the free atom. The solid line is the reference to indicate the values where there will not be any perturbation of the atomic splitting caused by the presence of the MgO(OOl) surface.

Finally, one can easily show that, while the "high" and "low spin" forms of one and the same species in a fixed geometry are related in a "ground versus excited state" sense, the optimal geometries of the two states need not be (and, most often, are not) Identical. An often cited paradigm is the fact that NiX has a "low spin" form but a "high spin" form with either of them becoming the... 

The DC magnetic susceptibihty of die complex measured at 1000 Oe from 1.8 to 300 K suggests diat at low temperature, a well-defined high-spin groimd state is almost exclusively thermally populated. The Curie Weiss fitting result of xmT versus T above 30 K indicates dominant antiferromagnetic interactions between spin carriers. The AC susceptibility of the complex over 1-1500 Hz from 1.8 to 3K indicates that the out-of-phase susceptibility displays frequency dependence, but none of the curves reaches a peak at 1.8 K. The DC magnetization decay method determined the effective barrier of 18.4 K and the relaxation time constant of 2 X 10 s. As Gd ion is an isotropic spin ion, the major anisotropy contribution comes from the Mn + ion, which is the most important anisotropy source of SMMs and SCMs. 

Pierloot, K., 8c Vancoillie, S. J. (2008). Relative energy of the high-(T-5(2g)) and low-((l)A(lg)) spin states of the ferrous complexes [Fe(L)(NHS4)] CASPT2 versus density functional theory. Journal of Chemical Physics, 128, 034104. 

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