question_answer 5)

Explain on the basis of valence bond theory that [Ni(CN4)]2– ion with square planar structure is damagnetic and the [NiCl4]2– ion with tetrahedral geometry is paramagnetic.

Answer:

[Ni(CN)4]2?. Nickel in this complex ion is in the +2 oxidation state. CN? ion is a strong ligand and cause pairing of unpaired electrons. dsp2?hybrid orbitals accommodate four pairs of  electrons from fourgroups and the resulting complex is square planar and is diamagnetic since no unpaired electron is present. Tetrahloronickelate (II) ion. Nickel in this complex is in the +2 oxidation state. The vacant 4s-orbital and three 4p-oprbitals hybridise to give four equivalent sp3hybridised orbitals. Four pairs of electrons, one from each ion occupy the four vacant hybrid orbitals so produced. The resulting complex has a tetrahedral geometry and is paramagnetic because of two unpaired electrons.