Question

What type of structural isomers are [Pt(OH)₂(NH₃)₄]SO₄ and [PtSO₄(NH₃)₄](OH)₂? How will you identify the isomers with a chemical test?

Answer 1

1. The compounds Pt(OH)₂​(NH₃​)₄​SO₄ and PtSO₄​(NH₃​)₄​(OH)₂ are examples of ionization isomers, a type of structural isomerism.
2. In the first complex, the hydroxide ions (OH⁻) are present inside the coordination sphere, while the sulfate ion \[\ce{(SO^2-_4)}\] acts as the counterion.
3. In the second complex, the sulfate ion is coordinated to the platinum atom within the coordination sphere, and the hydroxide ions are present outside as counterions.
4. These isomers can be identified by a simple chemical test:
   When barium chloride solution (BaCl₂) is added to a solution of Pt(OH)₂​(NH₃​)₄​SO₄, a white precipitate of barium sulfate (BaSO₄) is formed, indicating the presence of free \[\ce{SO^2-_4}\] ions.
5. However, when BaCl₂ is added to PtSO₄​(NH₃​)₄​(OH)₂, no precipitate is formed because the sulfate ion is bound to the metal and is not free in solution.
6. Additionally, PtSO₄​(NH₃​)₄​(OH)₂ will turn red litmus paper blue, showing basic nature due to the presence of free OH⁻ ions, whereas Pt(OH)₂​(NH₃​)₄​SO₄ will not show basicity as the hydroxide ions are coordinated.