Question

Identify the coordination sphere in the compound K4[Fe(CN)6].

(a) K^+

(b) Fe^2+

(c) [Fe(CN)6]^4-

(d) CN^–

I have been asked this question during an interview.

Origin of the question is Definitions topic in chapter Coordination Compounds of Chemistry – Class 12

Answer 1

Correct answer is (c) [Fe(CN)6]^4-

To explain I would say: The coordination sphere refers to the square bracket within which the central atom/ion and the groups attached to it are enclosed. This is a non-ionisable group as compared to the entity outside the bracket, which is ionisable and is known as the counter ion.