. Low spin octahedral complexes of nickel are not known

Explain the following

(i) Low spin octahedral complexes of nickel are not known.

(ii) The -complexes are known for transition elements only.

(iii) CO is a stronger ligand than NH3 for many metals.

                                                                  OR

Compare the following complexes with respect to structural shapes of units, magnetic behaviour and hybrid orbitals involved in units

(i) [Ni(CN)₄ ] ^2-

(ii) [NiCl₄ ] ^2-

(iii) [CoFe₆ ] ^3-

[At. Nos,: Ni = 28; Co = 27]