Question

${\left[Fe\right(H}_{2}O{)}_6{]}^{2+}$ and $\left[Fe\right(CN{)}_6{]}^{4-}$ differ in :

• A. geometry, magnetic moment
• B. magnetic moment and colour
• C. geometry and hybridisation
• D. None of the above

Answer 1

Answer: (B)

magnetic moment and colour

The geometries of both the complexes will be same because there coordination numbers are 6 and hence both will have octahedral geometry. The magnetic moment will change because in $\left[Fe\right(H_{2}O{)}_6{]}^{2+}$ the ligand is $H_{2}O$ which is a weak field ligand hence pairing won't take place in this molecule and hence will be high spin, high magnetic moment while in $\left[Fe\right(CN{)}_6{]}^{4-}$ CN is the ligand which is strong field ligand and hence will cause pairing and therefore has low magnetic momment. Also, because of the difference in unpaired electrons the colour of the complex will also be different and hence, the correct option is B.