Chemistry Reference
In-Depth Information
2P
z
s
P
x,y
s
2S
s
P
s
P
x,y
s
P
s
P
z
s
1P
z
s
S
s
1P
z
s
S
s
Au
4
L
4
2
+
2 AuL
1
S
s
Edge
bridges
Au
6
L
6
2
+
Fig. 9 Interaction diagram for the addition of two capping gold fragments to the central gold
tetrahedron. This leads to a prolate edge-bridged structure
3.3
Introduction of Interstitial Atoms
Figure
10
illustrates the skeletal molecular orbitals for octahedral [Au
6
(PPh
3
)
6
]
2
which has a closed shell electronic configuration [S
σ
]
2
[P
σ
]
6
, but has a destabilising
double negative charge. It is therefore not surprising that such a cluster has never
been isolated. An alternative way of satisfying the closed shell electronic require-
ments and retaining a positive charge on the cluster is possible if an interstitial atom
is introduced. For an octahedral gold cluster an additional gold atom is too large to
satisfy the steric requirements of the interstitial cavity, but a small main group atom,
e.g. C, N or O, is able to satisfy these steric requirements. Figure
11
gives the
relevant interaction diagram for octahedral [Au
6
C(PPh
3
)
6
]
2+
and an interstitial
carbon atom, which contributes just the right number of electrons to lead to a
[S
σ
]
2
[P
σ
]
6
pseudo-spherical ground state configuration. It is noteworthy that this
