question_answer

The diamagnetic species is:

A) \[{{[Ni{{(CN)}_{4}}]}^{2-}}\]

B)        \[{{[NiC{{l}_{4}}]}^{2-}}\]             

C) \[{{[CoC{{l}_{4}}]}^{2-}}\]    

D) \[{{[Co{{F}_{6}}]}^{2-}}\]

Correct Answer: A

Solution :

The decreasing order of strength of ligands is \[\underbrace{CO>C{{N}^{-}}>NO_{2}^{-}>N{{H}_{3}}>}_{\begin{smallmatrix}  Strong\,field\,ligand \\  cause\,pairitng\,of\,electrons \end{smallmatrix}}\]                                \[\underbrace{{{H}_{2}}O>{{F}^{-}}>C{{l}^{-}}>B{{r}^{-}}>{{I}^{-}}}_{\begin{smallmatrix}  Weak\,field\,ligand\,does \\  not\,cause\,parining \end{smallmatrix}}\] \[N{{i}^{2+}}\] in presence of \[C{{N}^{-}}\] \[n=0\] (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, \[s{{p}^{3}}{{d}^{2}}\] hybridisation