Question

The diamagnetic species is

• A. $[Ni(CN{)}_4{]}^{2-}$
• B. $[NiC{l}_4{]}^{2-}$
• C. $[CoC{l}_4{]}^{2-}$
• D. $[Co{F}_6{]}^{3-}$

Answer 1

Answer: (A)

$\underset{\text{Strong field ligand cause pairing of electrons}}{\underbrace{CO>C{N}^{-}>N{O}_2^{-}>N{H}_3>}}$
$\underset{\text{Weak field ligand does not cause pairing }}{\underbrace{H_{2}O>F^{-}>C{l}^{-}>B{r}^{-}>I^{-}}}$

$n=0$ (diamagnetic)
$ds{p}^2$ hybridisation, low spin complex.
$N{i}^{2+}$ in presence of weak ligand $C{l}^{-}$

$n=2$, paramagnetic
$s{p}^3$, hybridisation, high spin complex.
$C{o}^{2+}$ in presence of weak ligand $C{l}^{-}$

$n=3$, paramagnetic, $s{p}^3$ hybridisation
$C{o}^{2+}$ in presence of weak ligand $F^{-}$

$n=5$, paramagnetic, $s{p}^3{d}^2$ hybridisat