Question

For the complex [Fe(en)₂Cl₂]Cl, identify:

1. the oxidation number of iron.
2. the hybridisation and the shape of the complex.
3. the magnetic behaviour of the complex.
4. whether there is an optical isomer of the complex? If so draw its structure.
5. IUPAC name of the complex. (At. no. of Fe = 26)

Answer 1

(a) Let the oxidation number of iron be x. The ethylenediamine (en) is neutral, contributing 0 charge. Each chloride ion (Cl⁻) contributes–1 charge. Thus,

x + 0 + 2(–1) + (−1) = 0

x − 3 = 0

x = +3

∴ Oxidation number of iron, x = +3

(b) The two monodentate and two bidentate ligands make up the complex. Consequently, the shape will be octahedral, and the hybridization will be d²sp³.

(c) The oxidation state of iron is +3, resulting in the electron configuration of Fe³⁺: d⁵ given that the atomic number of Fe is 26. The presence of one unpaired electron in the d-orbital renders the complex paramagnetic.

(d) The cis-isomer of [Fe(en)₂Cl₂]Cl exhibits optical isomerism as it possesses non-superimposable mirror images resulting from the configuration of the chloride ions. The trans-isomer exhibits no optical isomerism due to its absence of chirality.

(e) Dichloridobis(ethane-1, 2-diamine)iron(II)chloride.