Chemistry Reference
In-Depth Information
H
H
H
H
H
H
-H
+
H
H
H
H
H
H
H
H
H
H
Cp
-
Cp
H
M
M
M
[all C-M distances
are equivalent]
π
-bonded
σ
-bonded
N
HH
N
N
H
M
M
N
N
N
M
H
H
H
N
H
H
N
N
H
a Cp
-
ligand also occupies
an octahedral face
two N-N-N ligands
each coordinated to a face
the classic M(Cp)
2
'sandwich' compound
Figure 2.26
Formation and coordination of H
5
C
5
−
as a
-bonded ligand and as a
-bonded ligand. In the latter
mode, the ligand occupies the face of an octahedron in the same way that a conventional cyclic
triamine does.
orbital model is more useful. In this field we also see an example of a rare cationic ligand,
NO
+
. With organometallic chemistry such an extensive and demanding field in its own
right, we shall deliberately limit our discussion of these somewhat unusual ligands and
their compounds in this introductory textbook. However, there are aspects of their mode of
coordination and spectroscopic properties that have driven extension of bonding models,
and this will be addressed in Chapter 3.
Concept Keys
Metal ions are almost invariably met with a set of coordinated ligands, each of which
provides one or more lone pairs of electrons to make one or more covalent bonds.
Denticity defines the number of donor groups of a ligand that are coordinated. Apart
from one (monodentate), those providing two (didentate) or more (polydentate)
donors may involve chelate ring formation. For each chelate ring, two linked donor
groups bind the central atom, forming a cyclic unit that includes the central atom.
Usually, the higher the denticity, the more stable is the complex formed.
