Which of the following species do not exist?

Which of the following species do not exist?
  1. $\left[\mathrm{SiF}_6\right]^{2-}$
  2. $\left[\mathrm{SiCl}_6\right]^{2-}$
  3. $\left[\mathrm{GeCl}_6\right]^{2-}$
  4. $\left[\mathrm{SiF}_5\right]^{-}$

Solution

$\left[\mathrm{SiCl}_6\right]^{2-}$ does not exist. The chlorine atom is much larger than fluorine which does not allow the six $\mathrm{Cl}$ atoms to surround the silicon due to repulsion between $\mathrm{Cl}$ atoms. Hence, due to interelectronic repulsions between $\mathrm{Cl}$ atoms, the compound is unstable and does not exist.

Asked in: AP EAMCET 2021 (24 Aug Shift 2)

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