Cis- Trans Isomerism in Complex Ions

Stereoisomerism: Complex ions display two types of stereoisomerism: cis- trans isomerism AND
optical isomerism.
 Cis- Trans Isomerism: Some square planar and octahedral show show cis- trans isomerism. In
complex ion, no double bond needed to restrict rotation. Instead the shape of complex holds
groups in different orientations about central ion.
 Cis- Trans in Square Planar: Cis- trans found in square planar complexes with two pairs of
ligands attached to central metal ion.
 In cis- isomer, the pair of ligands adjacent to each other, so coordinate bonds are 90 o apart. In
trans- isomer, the pair of ligands diagonally opposite each other, so coordinate bonds of the pair
are 180o apart.

Cis- Trans, Octahedral, Monodentate: Octahedral complexes containing four of one type of
ligand and two of another ligand may show cis- trans isomerism.
 In cis- isomer, two chloride ligands adjacent so bonds 90 o
apart. In trans- isomer, two chloride
ligands opposite ends so bonds 180o
apart.
 Cis- Trans, Octahedral, Bidentate: Octahedral complexes containing pair of bidentate ligands
and pair of monodentate ligands.
 Cis- Platin: Cis- platin used as anti- cancer drug. Inhibits tumour growth. Has side effects- kidney
damage. Works by formation of platinum complex inside cancerous cell which binds to DNA,
alters DNA structure and prevents DNA replication.