Chemistry Reference
In-Depth Information
z
C
3
C
2
C
2
y
C
2
x
Figure B.3
The coordinate system and symmetry operations for trigonal bipyramidal MX
5
,ofD
3h
symmetry
point group.
z
C
4
C
2
y
C
2
C
2
C
2
C
2
x
Figure B.4
The coordinate system and symmetry operations for square planar MX
4
,ofD
4h
symmetry point
group. Note that there is a C
2
operation colinear with a C
4
around the
z
axis.
in Figure B.5 for moving from square planar MX
4
(D
4h
) to square planar
trans
-MX
2
Y
2
(D
2h
) and
cis
-MX
2
Y
2
(C
2v
).
Distortions of common geometric shapes lead necessarily to changes in the point group.
For example, an octahedron (O
h
) can undergo three types of distortion. The first is
tetragonal
distortion
, involving elongation or contraction along a single C
4
axis direction, leading to
D
4h
symmetry. The second is
rhombic distortion
, where changes occur along two C
4
axes
Ta b l e B . 3
Point groups for several molecular shapes.
Coordination number
Stereochemistry
Point group
2
linear
D
∞
h
3
trigonal planar
D
3h
trigonal pyramidal
C
3v
t-shaped
C
2v
4
tetrahedral
T
d
square planar
D
4h
5
trigonal bipyramidal
D
3h
square-based pyramidal
C
4v
6
octahedral
O
h
trigonal prismatic
D
3h
