Coordination Compounds · Question 54

The correct increasing order of stability of the complexes based on 0 value is : I. [Mn(CN)6]3- II. [Co(CN)6]4- III. [Fe(CN)6]4- IV. [Fe(CN)6]3-

1. I < II < IV < III
2. IV < III < II < I
3. III < II < IV < I
4. II < III < I < IV

Answer

(1) I < II < IV < III

Solution

CN- is a strong-field ligand all four complexes are low spin.

CFSE = (-0.4 x + 0.6 y) 0 for t2gx egy

I. Mn3+, 3d4: t2g4 eg0 CFSE = -1.6 0

II. Co2+, 3d7: t2g6 eg1 CFSE = -2.4 + 0.6 = -1.8 0

III. Fe2+, 3d6: t2g6 eg0 CFSE = -2.4 0

IV. Fe3+, 3d5: t2g5 eg0 CFSE = -2.0 0

Greater the magnitude of CFSE, greater the stability.

Stability: I < II < IV < III

Answer: (1)