Complex ion A has one Fe$^{3+}$ ion together with six CN$^-$ ligands. Complex ion B has one Fe$^{2+}$ ion together with six CN$^-$ ligands. State the formulae of these two complex ions. Include the overall charge of each complex ion.
Explain why a solution containing complex ion A and a solution containing complex ion B do not have the same colour.
In complex ion A, each CN$^-$ ligand uses its carbon atom to bond to the Fe$^{3+}$ ion. State the type of bonding involved.
The complex ions do not all have the same geometry. Complex ion A is octahedral. Ag$^+$ ions form a linear complex with ammonia. Ni atoms form a tetrahedral complex with carbon monoxide molecules. In the monodentate carbon monoxide ligand, the carbon atom bonds to the nickel atom. Pd$^{2+}$ ions form a square planar complex with chloride ions. Complete Fig. 6.1 to show the geometry of each of these four ions, using three-dimensional bonds where needed. Mark one bond angle on each complex ion.