$15$Coordination compounds are widely present in the minerals, plant and animal worlds and are known to play many important functions in the area of analytical chemistry, metallurgy, biological systems and medicine. Alfred Werner's theory postulated the use of two types of linkages (primary and secondary) , by a metal atom/ion in a coordination compound. He predicted the geometrical shapes of a large number of coordination entities using the property of isomerism. The Valence Bond Theory (VBT) explains the formation, magnetic behaviour and geometrical shapes of coordination compounds. It, however, fails to describe the optical properties of these compounds. The Crystal Field Theory (CFT) explains the effect of different crystal fields (provided by the ligands taken as point charges) on the degeneracy of d-orbital energies of the central metal atom/ion. Answer the following questions:

(i)When a coordination compound $\displaystyle \mathrm{NiCl}_{2} \cdot 6 \mathrm{H}_{2} \mathrm{O}$ is mixed with $\displaystyle \mathrm{AgNO}_{3}$ solution, 2 moles of AgCl are precipitated per mole of the compound. Write the structural formula of the complex and secondary valency for Nickel ion.(ii)Write the IUPAC name of the ionisation isomer of $\displaystyle \left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5}\left(\mathrm{SO}_{4}\right)\right] \mathrm{Cl}$.(iii)Using Valence Bond Theory, predict the geometry and magnetic nature of:

(1) $\displaystyle \left[\mathrm{Ni}(\mathrm{CO})_{4}\right]$ (2) $\displaystyle \left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{3-}$ [Atomic number: $\displaystyle \mathrm{Ni}=28, \mathrm{Fe}=26$ ]

OR

(iii) Give reasons: (1) Low spin tetrahedral complexes are not formed. (2) $\displaystyle \left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right]^{3+}$ is an inner orbital complex whereas $\displaystyle \left[\mathrm{Ni}\left(\mathrm{NH}_{3}\right)_{6}\right]^{2+}$ is an outer orbital complex. [Atomic number: $\displaystyle \mathrm{Co}=27, \mathrm{Ni}=28$ ]

Chemistry · Coordination Compounds