Question

What are coordination compounds and how do they differ from double salts? Explain with examples.

Answer 1

Double salts and coordination compounds are molecular or addition compounds created by combining two or more salts in a stoichiometric ratio. A simple molecular ratio. However, the two exhibit different ionisation behaviours in aqueous solutions, as explained below. 

• Double salts: They are solid substances that break down into ions when dissolved in water. Therefore, double salts lose their identity in aqueous solutions. The following example demonstrates the nature of double salts.
  • Example: [Cu(NH₃)₄]²⁺ in this complex, the copper ion (Cu²⁺) is surrounded by four ammonia molecules (NH₃) acting as ligands. The coordination number of copper is 4, and the complex is tetrahedral.
• Coordination compounds: They are molecular or addition compounds that maintain their identity in aqueous solutions and exhibit properties distinct from their constituent ions. The example below demonstrates the nature of coordination compounds.
  • Example: K₄[Fe(CN)₆]·3KNO₃ (Potassium ferrocyanide with potassium nitrate) is a double salt. It consists of potassium ferrocyanide (K₄[Fe(CN)₆]) and potassium nitrate (KNO₃). In this, both salts retain their identities and do not form coordination bonds between ions.