Coordination Compounds Ques 51
51. Of the following complex ions, which is diamagnetic in nature?
[2011]
(a) $[NiCl_4]^{2-}$
(b) $[Ni(CN)_4]^{2-}$
(c) $[CuCl_4]^{2-}$
(d) $[CoF_6]^{3-}$
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Answer:
Correct Answer: 51.(b)
Solution:
(b) $Ni^{2+}=3 d^{8} 4 s^{\circ}$
Since, the coordination number of $Ni$ in this complex is 4 , the configuration of $Ni^{2+}$ at first sight shows that the complex is paramagnetic with two unpaired electron. However, experiments show that the complex is diamagnetic. This is possible when the $3 d$ electrons rearrange against the Hund’s rule as shown below. This is in accordance with the fact that the ligand involved here is strong i.e., $CN^{-}$ion.
$Ni^{2+}$ (after rearrangement)
Hence, now $d s p^{2}$ hybridization involving one $3 d$, one $4 s$ and two $4 p$ orbitals, takes place leading to four $d s p^{2}$ hybrid orbitals, each of which accepts four electron pairs from $CN^{-}$ion forming $[Ni(CN)_4]^{2-}$ ion.
$[Ni(CN)_4]^{2-}$
Thus, the complex is diamagnetic as it has no unpaired electron.
BETA
