Which complex among the following has the highest value of spin only magnetic moment?…
Which complex among the following has the highest value of spin only magnetic moment?
\(\left[\mathrm{Fe}(\mathrm{CN})_6\right]^{3-},\left[\mathrm{Fe}(\mathrm{CN})_6\right]^{4-},\left[\mathrm{Ni}(\mathrm{CN})_4\right]^{2-}\), \(\left[\mathrm{NiCl}_4\right]^{2-}\)
\(\left[\mathrm{Fe}(\mathrm{CN})_6\right]^{3-}\)
\(\left[\mathrm{Fe}(\mathrm{CN})_6\right]^{4-}\)
\(\left[\mathrm{Ni}(\mathrm{CN})_4\right]^{2-}\)
\(\left[\mathrm{NiCl}_4\right]^{2-}\)
Solution
(a) \(\left[\mathrm{Fe}(\mathrm{CN})_6\right]^{3-}\) has \(d^2 s p^3\) (inner \(d\) - complex) hybridisation with one electron unpaired.
(b) The \(\mathrm{Fe}^{2+}\) ion in \(\left[\mathrm{Fe}(\mathrm{CN})_6\right]^{4-}\) has outer electronic configuration of \(3 d^6\). The complex is a low spin complex. It contains 0 unpaired electrons with magnetic moment of \(0 \mathrm{BM}\) Therefore, under the influence of the octahedral crystal field, the possible electronic arrangement of \(\mathrm{Fe}\) (II) ion is \(t_{2 g}^6, e_g^0\).
(c) \(\left[\mathrm{Ni}(\mathrm{CN})_4\right]^{2-}\) is a square planar geometry formed by \(d s p^2\) hybridisation. \(\left[\mathrm{Ni}(\mathrm{CN})_4\right]^{2-}\) is diamagnetic, so \(\mathrm{Ni}^{2+}\) ion has \(3 d^8\), outer configuration with two unpaired electrons.
For the formation of the square planar sructure by structure by \(d s p^2\) - hybridisation, two unpaired \(d\)-electrons are paired up due to energy made available by the approach of ligands, making one of the \(3 d\)-orbitals empty.
\(\therefore \mathrm{Cl}^{-}\)is a weak ligand so, there is no pairing of electrons.
Number of unpaired \(=2\)
Hence, the correct option is (d).
