Question

The diamagnetic species is

• A. $[Ni(CN)_4]^{2-}$
• B. $[NiCl_4]^{2-}$
• C. $[CoCl_4]^{2-}$
• D. $[CoF_6]^{3-}$

Answer 1

Answer: (A)

$[Ni(CN)_4]^{2-}$

Answer 2

$\underbrace{ CO > CN ^{-}> NO _{2}^{-}> NH _{3}>}_{\text{Strong field ligand cause pairing of electrons}}$ $\underbrace{ H _{2} O > F ^{-}> Cl ^{-}> Br ^{-}> I ^{-}}_{\text {Weak field ligand does not cause pairing }}$ $n=0$ (diamagnetic) $d s p^{2}$ hybridisation, low spin complex. $Ni ^{2+}$ in presence of weak ligand $Cl ^{-}$ $n=2$, paramagnetic $s p^{3}$, hybridisation, high spin complex. $Co^{2+}$ in presence of weak ligand $Cl ^{-}$ $n=3$, paramagnetic, $s p^{3}$ hybridisation $Co ^{2+}$ in presence of weak ligand $F ^{-}$ $n=5$, paramagnetic, $s p^{3} d^{2}$ hybridisat