CBSE Class 12 · 2008 · Delhi · Coordination CompoundsShort Answer

a) What is a ligand? Give an example of a bidentate ligand.
b) Explain how the two complexes of nickel, [Ni(CN)

_{4}

]

^{2 -}

and Ni(CO)

_{4}

, have different structures but do not differ in their magnetic behaviour. (Ni = 28)

Solution

(a) A ligand is an ion or molecule that donates a lone pair of electrons to the central metal atom/ion to form a coordinate bond. Bidentate example: ethane-1,2-diamine (en), which binds through both N atoms.
(b) [Ni(CN)

_{4}

]

^{2 -}

: Ni

^{2 +}

= 3d

^{8}

; strong-field CN

^{-}

pairs the electrons, giving \textbf{dsp

^{2}

— square planar}.
Ni(CO)

_{4}

: Ni(0) = 3d

^{8}

^{2}

; the very strong-field CO forces the 4s pair into 3d (3d

^{10}

), and the ligands use \textbf{sp

^{3}

— tetrahedral}.
In both cases every electron is paired (0 unpaired), so despite the different shapes both complexes are \textbf{diamagnetic}.

CBSE Class 12 Board · 2008 · Delhi · Subjective

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CBSE Class 12 · 2008 · Delhi · Coordination CompoundsShort Answer

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