04 INTRODUCTION TO TRANSITION METALS CHEMISTRY AND COORDINATION COMPOUNDS (PART 3).pdf

Introduction to Transition Metals
Chemistry and Coordination
Compounds

Constitutional Isomers of Coordination
Compounds
Compounds with the same formula, but with the atoms
connected differently, are constitutional isomers .
Coordination isomers occur when the composition of
the complex ion, but not the compound, is different.
- This can occur by the exchange of a ligand and a counter ion, or by
the exchange of ligands.
Linkage isomers occur when the composition of the
complex ion is the same but the ligand donor atom is
different.
- Some ligands can bind to the metal through either of two donor
atoms .

Linkage Isomers
The nitrite ion can bind either through the N atom or either one of
the O atoms.

Ligands that have more than one donor atom

Stereoisomers of Coordination
Compounds
Stereoisomers are compounds that have the same atomic
connections but different spatial arrangements of their
atoms.
Geometric or cis-trans isomers occur when atoms or
groups can either be arranged on the same side or on
opposite sides of the compound relative to the central
metal ion.
Optical isomers ( enantiomers ) are nonsuperimposable
mirror images of each other.

Geometric Isomerism
In the cis isomer, identical ligands are adjacent to each other, while in
the trans isomer they are across from each other.
The cis isomer ( cisplatin ) is an antitumor agent while the trans
isomer has no antitumor effect.
The cis and trans isomers of [Pt(NH
3
)
2
Cl
2
].

Geometric Isomerism
The cis and trans isomers of [Co(NH
3
)
4
Cl
2
]
+
.
Note the placement of the Cl – ligands (green spheres).
cis
trans

Optical Isomerism in an Octahedral Complex Ion
chiral
achiral

Optical Isomerism
• Chiral molecules are optically active.
• Rotate the plane of polarized light.
Polarimeter

Important Types of Isomerism in
Coordination Compounds

Draw stereoisomers for each of the following and
state the type of isomerism each exhibits:
(a) [Pt(NH
3
)
2
Br
2
] (square planar)
(b) [Cr(en)
3
] 3+

SOLUTION:

(b) Ethylenediamine (en) is a bidentate ligand. The Cr 3+ ion has
a coordination number of 6 and an octahedral geometry, like
Co 3+ . The three bidentate ligands are identical, so there is