CBSE Class 12 · 2000 · All India · Coordination CompoundsShort Answer

Among [Ag(NH

_{3}

)

_{2}

]Cl, [Ni(CN)

_{4}

]

^{2 -}

and [CuCl

_{4}

]

^{2 -}

, which:
i) has square planar geometry?
ii) remains colourless in aqueous solution, and why?
[Atomic numbers: Ag = 47, Ni = 28, Cu = 29]

Answer: (i) [Ni(CN)₄]²⁻ (dsp², d⁸ with strong-field CN⁻). (ii) [Ag(NH₃)₂]Cl — Ag⁺ is 4d¹⁰ (filled d-shell, no d–d transition).

Solution

(i) [Ni(CN)

_{4}

]

^{2 -}

: Ni

^{2 +}

(3d

^{8}

) with the strong-field CN

^{-}

pairs its electrons, freeing one 3d orbital — dsp

^{2}

hybridisation, square planar.
(ii) [Ag(NH

_{3}

)

_{2}

]Cl stays colourless: Ag

^{+}

is 4d

^{10}

— a completely filled d-subshell permits no d–d transition, so no visible light is absorbed.
([CuCl

_{4}

]

^{2 -}

, with Cu

^{2 +}

^{9}

, is coloured.)

CBSE Class 12 Board · 2000 · All India · Subjective