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the Mn.10.1.0 system with the two model systems where either M-M bonding or
also the effect of the carbonyl ligands was disabled. The metal sources for the M-M
bonded systems are comparatively more negative because of the enhanced decrease
in the charge concentration within the metal atomic M shell due to M-M bonding.
It is worth emphasizing, however that, irrespective of the lack or presence of a
bcp, the picture of a nonlocalized M-M interaction with features quite different
from those of a conventional covalent bond emerges. The electron sharing between
metals is small through the whole series [
d
(M, M
0
)
0.29-0.44] and quite far from
one, and the S%(M) values are also small, with the electron density at the M-M bcp
or mp being largely determined by atoms other than the metals. As anticipated
earlier, the nonvanishing
d
(M,M
0
) values for the systems with no M-M bond is a
necessary consequence of the indirect 3c-2e M-M bonding through the bridging
ligands [
60
,
94
].
The unbridged (D
3d
, Co.8.1.0) and the double-bridged (C
2v
, Co.8.1.2) Co
2
(CO)
8
isomers offer the possibility to compare direct and indirect M-M bonding features
for two systems having the same metal atoms and number of CO ligands. Figure
10
shows that for both systems the electron density at bcp or at the Co-Co mp is
essentially determined by the carbonyl groups and in particular by the carbonyl
ΒΌ
Fig. 10 Source function percentage contributions at the Co-Co midpoint (
left
) and local source
(LS),
r
2
r
and
r
profiles along the Co-Co internuclear axis (
right
) for the unbridged D
3d
(
top
)
and the double-bridged C
2v
(
bottom
)Co
2
(CO)
8
isomers. Bcp and midpoint locations are denoted
by a star and a triangle, respectively. The Co-Co bcp or midpoint is used as reference point for the
LS profiles [adapted from Fig. 7, with permission from [
14
],
http://pubs.rsc.org/en/Content/
ArticleLanding/2007/FD/b605404h
Copyright 2007, The Royal Society of Chemistry (RSC)]
