Using IUPAC norms write the formulae for the following:

(a) Potassium trioxalatoalumniate (III)

(b) Dichloridobis (ethane -1, 2-diamine) cobalt (III)

(a) The general steps to write the formula from the IUPAC name is as follows:

1. Identify the central atom and the ligands attached to it. Write the formula in the following order:

[Metal atom; anionic, neutral, cationic ligands]

2. Calculate the charge on the complex species:

Charge on complex species = Oxidation state of central atom/ion + total charge on ligands attached

3. If the calculated charge is positive, then complex species is cationic complex and the anions in the ionic sphere. If charge is negative, it is anionic complex and would contain cations in coordination sphere.

4. In case of cationic complex write the ionic sphere immediately after the coordination sphere while in case of an anionic complex write the ionic sphere immediately before the coordination sphere.

In this case as the name suggests trioxalatoalumniate implies that the central atom is aluminium and 3 oxalate ligands are attached to it.

Charge on species = +3 + (-2 × 3)

= 3 – 6

= -3

Thus the complex species can be represented as [Al (C₂O₄)₃]^-3.

So the ionic sphere contains potassium and to balance the charge we require 3 K⁺ ions in ionic sphere. So the given coordination compound is as follows:

K₃ [Al (C₂O₄)₃]

(b) The formula of the given compound is as follows:

[CoCL₂ {en} ₂]⁺

The ligand (en) also known as ethyl diamine is a neutral ligand and hence no charge is associated with it.

Charge on species = +3 + (2 × -1) + 0

= 3 – 2

= 1

So charge on the species is +1.

The formula of the given compound is as follows:

[CoCL₂ {en} ₂]⁺