Chemistry Reference
In-Depth Information
Fig. 10 Skeletal molecular orbitals for octahedral [Au
6
(PPh
3
)
6
]
2
simple theoretical analysis was first published in 1976 [
77
], and the existence of
[Au
6
C(PPh
3
)
6
]
2+
was confirmed by Schmidbaur and his co-workers in 1989
[
42
-
44
]. This compound had been isolated and structurally characterised
previously, but the interstitial carbon had not been identified. The introduction of
the interstitial atom strengthens the radial interactions significantly as a result of
effective overlaps between the carbon 2s and 2p orbitals and the matching S
σ
and P
σ
cluster molecular orbitals. In broad brush terms the stabilisation of the valence
orbitals of the central atom are stabilised by n
β
σ
/degeneracy of the molecular
β
σ
(s) ¼
β
σ
(p) ¼
β
σ
(d), the relative stabilisations are 6
β
σ
(s), 2
β
σ
(p),
orbitals. If
β
σ
(d). Therefore, the greatest stabilisation involves the s orbitals of the central
atom and increases as the number of metal atoms,
n
, increases. For filled shells the
stabilisation energies are independent of geometry as long as the ligand polyhedron
approximates to a sphere. It follows that gold clusters with main group interstitial
atoms are characterised by a pec of 12
n
+ 8 (sec 8) valence electrons, since each
AuPPh
3
fragment is associated with a filled d shell containing 10 electrons and a
bonding Au-P bonding molecular orbital.
and 3
