Gujarat BoardEnglish MediumSTD 12 ScienceChemistryCoordination Compounds4 Marks
Question
Explain magnetic property of coordination compound.
✓
Answer
→ Metal ions with upto three electrons in the d orbitals, like $Ti ^{3+}\left( d ^1\right) ; V ^{3+}\left( d ^2\right) ; Cr ^{3+}\left( d ^3\right) ;$ tuo vacant $d$ orbitals are available for octahed $d^3$ hybridization with 4 s and 4 p orbitals. → The magnetic behaviour of these free jons and their coordination entities is similar. → When more than three 3d electrons are present, the required pair of 3d orbitals for octahedral hybridization is not directly available (as a consequence of Hund's rule). → Thus, for $d ^4\left( Cr ^{2+}, Mn ^{3+}\right), d ^5\left( Mn ^{2+}, Fe ^{3+}\right), d ^6$ $\left( Fe ^{2+}, Co ^{3+}\right)$ cases, a vacant pair of d orbitals results only by pairing of 3 d electrons which leaves two, one and zero unpaired electrons, respectively. → The magnetic data agree with maximum spin pairing in many cases, especially with coordination compounds containing d6 ions. However, with species containing d4 and d5 ions there are complications. →$\left[ Mn ( CN )_6\right]^{3-}$ has magnetic moment of two unpaired electrons while $\left[ MnCl _6\right]^{3-}$ has a paramagnetic moment of four unpaired electrons. → $\left[ Fe ( CN )_6\right]^{3-}$ has magnetic moment of a single unpaired electron while $\left[ FeF _6\right]^{3-}$ has a paramagnetic moment of five unpaired electrons. → $\left[ CoF _6\right]^{3-}$ is paramagnetic with four unpaired electrons while $\left[ Co \left( C _2 O _4\right)_3\right]^{3-}$ is diamagnetic. → This apparent anomaly is explained by valence bond theory in terms of formation of inner orbital and outer orbital coordination entities. → $\left[ Mn ( CN )_6\right]^{3-},\left[ Fe ( CN )_6\right]^{3-}$ and $\left[ Co \left( C _2 O _4\right)_3\right]^{3-}$ are inner orbital complexes involving $d ^2 sp ^3$ hybridisation, the former two complexes are paramagnetic and the latter diamagnetic. → On the other hand, $\left[ MnCl _6\right]^{3-},\left[ FeF _6\right]^{3-}$ and $\left[ CoF _6\right]^{3-}$ are outer orbital complexes involving $sp ^3 d^2$ hybridisation and are paramagnetic corresponding to four, five and four unpaired electrons.
Need a full question paper?
Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.