We will analyze in the following effects related to the inner
reorganization of the individual fragment orbitals. The term explicitly
labeled as electrostatic interaction in Tables 4–6 refers only to
the Coulomb effects between fragments with frozen density,
namely with the central ion in a spherical shape and having the active
electrons smeared with equal populations in all the five d orbitals.
This is so for both schemes discussed in Figs. 1 and 3. The
switch between the behavior of eg and t2g orbital interaction channels,
when passing from complexes with negative ligands to the
series with neutral ligands, can be attributed to the role of electrostatic
dynamics during the bond formation. In the LFSE rationales
we consider only the perturbing role of the ligands against the
electrons accommodated on the metal ion, but in the total molecular
calculation we account also for the perturbing role of the metal
ion orbital distribution against the ligand frame, this effect
being enhanced in the case of charged ligands, as compared to
the neutral ones.
Thus, in the case of neutral aqua ligands, the part due to LFSE on
the metal ion prevails and the trends in orbital components are
similar to the upper placement of eg levels and lower t2g ones in
the LF diagrams. The |4n + 6m| coefficients of the LFSE for a
tn
2gemg
configuration, taken as abscissa in Fig. 1 grow in the sense
of progressive depopulation of the eg set, and occupation gain in
the t2g subshell. The transfer of the eg electrons populated in the
spherical fragment ion toward the t2g leads to the repulsion exerted
by the d-lobes aligned to x, y and z axis, towards the negative
ligands. The value of the stabilization energy resulted from the
electrostatic relaxation of the t3ðnþmÞ=5
2g e2ðnþmÞ=5
g spherical reference
to the actual tn
2gemg
configuration is proportional to the |4n + 6m|
LFSE factor. Apparently counter-intuitive with respect to the customary
perception, one may observe that the depopulation of
upper LF orbitals leads, in the numerical experiment of construction
from fragments, to a stabilizing effect, due to the preponderance
of electrostatic relaxation of the repulsion between d
electrons and the negatively charged ligands, which supersedes
the LF stabilization on the metal ion. From a certain perspective,
the effects discussed can be considered a byproduct of the choice
of starting with a spherically averaged metal ion fragment. However,
this choice and resulting consequences are not without physical
meaning, since the basic LFSE concept rely on the idea of a
spherically averaged reference.