Chemistry Reference
In-Depth Information
(a)
(b)
σ
d
H
2
H
5
C
2
H
2
H
1
H
3
H
1
H
6
σ
d
C
2
H
3
C
2
H
4
H
5
C
2
H
6
H
4
C
4
(c)
σ
v
σ
d
Cl
σ
v
L
L
M
L
L
Br
Figure 1.15
(a) An example dihedral plane
σ
d
for ethane in the staggered conformation and
the two C
2
axes it lies between. (b) A Newman projection view showing the
σ
d
plane bisects
the angle between the C
2
axes. (c) An example metal complex with no horizontal C
2
axes.
example of another pair of planes that only contain M and the halogen atoms, and reflect
cis
-L ligands into one another. This plane bisects the angle between the two
σ
v
planes and
so is labelled
σ
d
. The other
σ
d
plane would be perpendicular to the page.
Problem 1.1:
In Section 1.2.3, Figure 1.19 shows the structure of the square planar
complex [PtCl
4
]
2
−
, find and label all the proper rotation axes and planes of symmetry
for this structure. Remember to consider the full set of operations for high-order axes.
1.2.3 The Inversion Centre:
i
So far, we have looked at symmetry operations for which the corresponding elements are
the plane (a reflection operation) and a line (the rotation operation). The next symmetry
element is the
inversion centre,
labelled
i.
The operation of inversion leaves only a single
point unchanged, and so it is often referred to as a centre, or point, of symmetry. The
inversion operation is illustrated in Figure 1.16 with two pairs of points, A, A
and B, B
,
which represent atoms in a hypothetical molecule. For each pair, the points are equidistant
