Explain the following cases giving appropriate reasons: (i) Nickel does not form low spin octahedral complexes.

(i) Nickel does not form low spin octahedral complexes because ‘Ni’ has electronic configuration 3d⁸ 4s², in which two inner d-orbitals are not available which are required to form d²sp³ hybridization.

(ii) The p-complexes are known for the transition metals only because they have ‘sandwich’ structure in which the metal ion lies between two planar C₅H₅ rings. The bonding involves overlap of p-electrons of the C₅H₅ rings with unfilled d-orbital of the metal. So that all M–C bonds are identical for their stability.

(iii) Co²⁺is easily oxidised to Co³⁺in the presence of a strong ligand because in presence of strong ligand, the 3d electrons pair up leaving two orbitals empty to be involved in d²sp³ hybridisation.

Only one inner d orbital is available so d² sp³ hybridisation not possible.