Q1(e). Oxidation of Fe(II) and Mn(II)

Answer in brief

Oxidising Fe(II), d⁶, gives the relatively stable half-filled d⁵ Fe(III) configuration; oxidising Mn(II), d⁵, destroys that configuration.

Key points

• High-spin Fe(II) has one paired d electron beyond a half-filled shell. Removal gives five singly occupied d orbitals and increased exchange stabilisation.
• Mn(II) already has the stable high-spin d⁵ arrangement. Removal gives Mn(III), d⁴, losing half-filled-shell stabilisation.
• Thus Mn(III)/Mn(II) has a more positive aqueous reduction potential than Fe(III)/Fe(II), and Mn(II) is harder to oxidise under comparable conditions.