Spin Properties of Transition-Metallorganic Self-Assembled Molecules Page: 4 of 47
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SH
N N
[ Fe
N>X
SH
Figure 1: A representative conjugated metallorganic molecule containing an ion, Fe III.
The surrounding ligands are phenanthroline, a strong ligand used in various complexes.
One of the phenanthroline ligands is decorated by two dithiol (i.e., SH) groups at the ends
for good contact with the electrodes.
configurations: one has a high spin of 5/2 if the exchange interaction of d electrons
(Hunds rule) is stronger than the ligand field A; the other has a low spin of 1/2 with all
5 electrons occupying t2g levels if the exchange interaction is much weaker than A. From
the first-principles calculations we find that it is the latter scenario that occurs in this
kind of molecule and that A is very large (A = 3.2 eV for Fe3+ and 2.2 eV for Mn2+),
indicating that eg states can be safely neglected in studying spin states in these TMSAMs.
Hole representation. We have noticed that 5 d electrons occupying 3 t2g levels are
equivalent to 1 hole in a closed t2g shell. So instead of the conventional electron represen-
tation we use the hole representation, which greatly simplifies the Hamiltonian. In the
hole representation, the spin-orbit coupling has the opposite sign compared to that in the
electron representation.
Small splitting between t2g levels. The octahedral symmetry of the ligand field is
slightly broken in the TMSAM because one ligand has two (SH) groups but the other two
ligands do not. A careful analysis indicates that this small difference can be described by
a tetragonal distortion, which creates an energy splitting between doy and the degenerate
d~z and dyz. From the first-principles results, the splitting in these molecules is about
0.02 eV.3
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Yu, Zhi Gang. Spin Properties of Transition-Metallorganic Self-Assembled Molecules, report, June 30, 2010; United States. (https://digital.library.unt.edu/ark:/67531/metadc1014357/m1/4/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.