Question

During the reductions

A.    Fe(CN)₆^3-    →     Fe(CN)₆^2-

B.    Co(NH₃)₆³⁺ → Co(NH₃)₆²⁺

the metal–ligand distance changed as follows:

		A) metal–ligand distance shortens equally in both cases.
		B) metal–ligand distance lengthens equally in both cases.
		C) metal–ligand distance lengthens more in reduction A more than in reduction B
		D) metal–ligand distance lengthens more in reduction B more than in reduction A

Answer 1

The option (c) is correct. Metal-ligand distance lengthens more in reduction A more than in reduction B. It is because, CN^- is good pi acceptor and as a result, good pi donation is there from metal to the ligand. However, there NH₃ is a weaker pi acceptor, hence the pi back donation is not prominent. As a result, in case cyanide complex, the reatants side has a higher negative charge compored to the product side. So more back donation from metal to ligand pi orbitals compared to product side. Consequently, metal ligand distance is shoreter in the reactant side compred to the product side.