Synthesis of tris(ethylenediamine)nickel(II) from Ni(II) salt, ethylenediamine and sodium thiosulfate.

 Synthesis of Tris(ethylenediamine)nickel(II)

Aim

To synthesize tris(ethylenediamine)nickel(II) complex $[Ni(en)_3]^{2+}$ from a Ni(II) salt, ethylenediamine and sodium thiosulfate.

---

Principle

Ethylenediamine (en) is a bidentate ligand containing two nitrogen donor atoms. It coordinates with Ni²⁺ ions forming a stable octahedral complex tris(ethylenediamine)nickel(II).

Three ethylenediamine molecules coordinate with one Ni²⁺ ion through nitrogen atoms forming the complex ion $[Ni(en)_3]^{2+}$. Sodium thiosulfate is used to stabilize the complex and prevent formation of unwanted precipitates.

Reaction

$$Ni^{2+} + 3en \rightarrow [Ni(en)_3]^{2+}$$

Where
en = Ethylenediamine

Requirements

Chemicals

Nickel(II) chloride / Nickel(II) sulphate,Ethylenediamine (en), Sodium thiosulfate, Distilled water, Ethanol

Apparatus

Beaker, Glass rod, Measuring cylinder, Funnel, Filter paper, Water bath

Procedure

1. Dissolve about 2 g of nickel(II) salt in 15–20 mL distilled water in a beaker.

2. Add a few mL of sodium thiosulfate solution to the nickel solution and stir well.

3. Add excess ethylenediamine slowly with constant stirring.

4. Heat the mixture gently on a water bath for 10–15 minutes.

5. The solution turns deep violet or purple, indicating formation of the complex.

6. Allow the solution to cool slowly.

7. Crystals of tris(ethylenediamine)nickel(II) separate out.

8. Filter the crystals using filter paper.

9. Wash the crystals with cold ethanol and dry between filter papers.

Observation

Observation	Result
Colour of nickel salt solution	Green
Colour change after adding ethylenediamine	Violet / purple
Nature of crystals obtained	Violet crystalline solid

Result

Tris(ethylenediamine)nickel(II) complex $[Ni(en)_3]^{2+}$ was successfully synthesized as violet crystals.