Question

Which of the following species is not stable ?

• A. \([SiF_6]^{2-}\)
• B. \([GeCl_6]^{2-}\)
• C. \(Sn(OH)_6]^{2-}\)
• D. \([SiCl_6]^{2-}\)

Answer 1

The Correct Option is D

To determine which species is not stable among the provided options, we need to consider the stability of hexacoordinate complexes formed by silicon (Si) and other related elements such as germanium (Ge) and tin (Sn) with different ligands like fluoride (\(F^-\)), chloride (\(Cl^-\)), and hydroxide (\(OH^-\)).

1. [SiF_6]^{2-}: Fluoride is a small and highly electronegative ligand, which forms stable complexes with silicon. The highly polarizing fluoride ions stabilize the silicon in a hexacoordinate environment. Thus, [SiF_6]^{2-} is stable.
2. [GeCl_6]^{2-}: Germanium can form stable complexes with chloride ions. Germanium, being larger than silicon, can accommodate the larger chloride ions relatively well. Hence, [GeCl_6]^{2-} is stable.
3. [Sn(OH)_6]^{2-}: Tin forms stable hydroxide complexes due to the suitability of its ionic size and charge. Therefore, the complex [Sn(OH)_6]^{2-} is stable.
4. [SiCl_6]^{2-}: Silicon has a smaller ionic radius compared to germanium and tin, and the larger chloride ions do not stabilize the hexacoordinate structure effectively. Silicon typically does not form stable hexachloride complexes because the larger chloride ions cause steric hindrance and instability. Hence, [SiCl_6]^{2-} is not stable.

Conclusion: The species [SiCl_6]^{2-} is not stable due to the inability of silicon to effectively accommodate six large chloride ions in a stable hexacoordinate structure.