Explain on the basis of Valance Bond Theory that diamagnetic [Ni(CN)4 ]2- has square planar structure and paramagnetic [Ni(CN)4 ]2- ion has tetrahedral geometry ?
Ans.In the complex [Ni(CN)4]2−[Ni(CN)4]2−, the oxidation state of nickel is +2+2 and it has d8d8 configuration in its outer shell. Four CN−CN−attached to the centre nickel metal indicates that it can either has a tetrahedral or square planar geometry. As the CN−CN−is a strong field ligand, the unpaired 3 d3 d electrons gets paired due to the cyanide ion ligand. So, this complex will have a dsp 22 hybridization, making its shape as square planer. In the complex [NiCl4]2−[NiCl4]2−, the chloride ion is a weak field ligand. Hence, the unpaired 3 d3 d electrons will not be paired and this complex will have a sp3sp3 hybridization making its shape as tetrahedral.
