Question

Until the discoveries of Werner it was thought that the presence of carbon in a compound was required for it be optically active. Werner prepared the following compound containing ions as bridging groups and then separated the optical isomers.

a. Draw structures of the two optically active isomers of this compound.

b. What are the oxidation states of the cobalt ions?

c. How many unpaired electrons are present if the complex is the low-spin case?

Short answer

Two optically active isomers are

Where,$\mathrm{CoA}=\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_4$

b. The cobalt ions are in +3 oxidation state

c. 4 unpaired electrons are present in central cobalt of the complex

Step-by-step solution

Optical isomers

Optical isomers are formed by the complex with respect to the bridged ligands. The isomers are non-superimposable mirror images of each other. Hence the complex rotates plane polarised light.

Where

Determine the oxidation state

The cobalt ions present in the complex have +3 oxidation states. As the charge on the complex ion is balanced by six chloride ions, the cobalt ions in the coordination sphere are present in +3 oxidation states.

Determine the unpaired electron

The cobalt (+3) has 4 unpaired electrons for low spin case. As the hydroxide ion is relatively weak field ligand (from spectrochemical series), the number of unpaired electrons in the central cobalt of the complex is four.