1
$\begingroup$

I recently came across this question while studying Solid State.
The coordination no. of [Ni(CN)4]2- is 4 as Ni is bonded to 4 CNs and is planar in structure.Hence its Limiting Radius Ratio must be between 0.225 and 0.414 . But the answer given in the book is 0.414 to 0.732 (which is the limiting radius ratio for coordination no. 6) .
How is this true?Some sites agree with my answer .
Is the answer given in the book wrong or have I made any mistake in the reasoning?

$\endgroup$
  • $\begingroup$ I've always calculated limiting radius ratio for ionic crystals. I'm not sure if such a thing exists for coordination compounds. $\endgroup$ – Berry Holmes May 10 '17 at 8:51
  • $\begingroup$ I have a hunch that the charge 2- on the ion has some role to play. I am not sure. And yeah you are right . Even I calculated only for ionic crystals not for coordination compounds $\endgroup$ – Sourabh Yelluru May 10 '17 at 8:52
  • $\begingroup$ If you insist, a cursory search tells me that the crystal radius of $\ce{CN-}$ is $\pu{1.77 Å}$, and the ionic radius for $\ce{Ni^2+}$ ion is $\pu{0.69 Å}$. $\endgroup$ – Berry Holmes May 10 '17 at 9:23
  • $\begingroup$ Then the radius ratio will be 0.3898 which agrees with my answer. $\endgroup$ – Sourabh Yelluru May 10 '17 at 9:28
1
$\begingroup$

Here, limiting radius ratio is for geometry of this complex is square planar because $\ce{CN-}$ is a strong field ligand and causes pairing of unpaired electrons. So we can relate that $\ce{Ni^2+}$ occupies a square planar void of the $\ce{CN-}$ lattice. The square planar void is a cross section of the octahedral void.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.