Question

Give reasons:
(I) \([ \text{Ni(CO)}_4 ]\) is diamagnetic whereas \([ \text{NiCl}_4 ]^{2-}\) is paramagnetic. [Atomic number: Ni = 28]
(II) CO is a stronger complexing agent than NH\(_3\).
(III) The trans isomer of complex \([ \text{Co(en)}_2\text{Cl}_2 ]^{+}\) is optically inactive.

Hint:

In square planar and octahedral complexes, the arrangement of ligands and the presence of strong or weak field ligands can determine magnetic properties and optical activity.

Answer 1

(I) In \([ \text{Ni(CO)}_4 ]\), Ni exhibits a stable low-spin electronic configuration with no unpaired electrons, resulting in diamagnetism. Conversely, in \([ \text{NiCl}_4 ]^{2-}\), Ni's higher oxidation state leads to unpaired electrons, causing paramagnetic behavior.
(II) CO's potent \(\pi\)-acceptor ability enables it to form stronger bonds with metal centers than NH\(_3\), a ligand with weaker field strength.
(III) The trans isomer of \([ \text{Co(en)}_2\text{Cl}_2 ]^{+}\) is optically inactive due to its symmetrical structure, precluding optical isomerism.