[Co(ampy)2(NH3)2]3+
The isomerism of this compound is quite complex due to the fact that 2-(aminomethyl)pyridine (ampy) is an asymmetric lignd. This ligand contains one pyridine-type donor atom (incorporated in the aromatic ring) and one ethylenediamine-type ligand. A total of eight stereoisomers are possible. These can be broken down into two groups, depending upon whether the chloride ions are cis or trans.

There are three sets of isomers in which the chloride ions are cis:
1. Two isomers (enantiomers) in which the -NH2 groups of the ampy ligands are mutually trans
2. Two isomers (enantiomers) in which the pyridine-type donor atoms are mutually trans
3.Two isomers (enantiomers) in which each -NH2 donor atom is trans to a pyridine-type donor atom

There are two isomers in which the chloride ions are trans:
4. One isomer in which the like nitrogen donors are trans to each other (no enantiomer)
5. One isomer in which the like nitrogen donors are cis to each other (no enantiomer)

-NH2 groupsare trans
(mirror image of molecule at right)

-NH2 groupsare trans
(mirror image of molecule at left)

Pyridine-type donor atoms are trans

Pyridine-type donor atoms are trans

Each -NH2 trans to pyridine-type donor
(mirror image of model at right)

Each -NH2 trans to pyridine-type donor
(mirror image of model at left)

Chloride ions are trans
Like nitrogen donors are trans

Chloride ions are trans
Like nitrogen donors are cis