Question

The observed effective magnetic moment of two octahedral complexes, K4[Mn(CN)6].3H2O(X) and K4[Mn( SCN)6] (Y) are 2.18 BM and 6.06 BM, respectively. Which of the following is correct?

I. X is low spin complex with two unpaired electrons

II. Y is high spin complex with 5 unpaired electrons

III. X is a high spin complex with two unpaired electrons

IV. Y is a low spin complex with 5 unpaired electrons

(A) I and III

(B) I, II

(C) I, II and IV

(D) I, II and III

Answer 1

Correct answer is (B) I, II

K4[Mn(CN)6].3H2O ⇒Mn2+ with CN = 6 & SFL

∴ Pairing will take place

⇒ Low spin complex with one unpaired electron.

K4[Mn( SCN)6] ⇒ Mn2+ with CN = 6 & WFL

∴ Pairing will not take place

⇒ High spin complex with five unpaired electrons.

So, only II statements is correct, which matches with none of given options.

So, question should be BONUS

However, from the available options, (B) seem best.