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Explain the structure of [Ni(CN)_(4)]^(2-) on the basis of valencebond theory. |
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Answer» Solution :(1) Tetracyanonickelate (II) ion, `[Ni(CN)_(4)]^(2-)` isananioniccomplex, oxidation stateof NIIS +2and thecoordination numberis 4. (2) Electronic configuration : `""_(28) Ni [Ar]^(18) 3d^(8) 4s^(2) 4p^(6)` Electronic configuration : `Ni^(2+) + [Ar]^(18) 3d^(8) 4s^(0) 4p^(0)` `Ni^(2)` (Groundstate)  (3)Since `CN^(-)` is a strong ligand, one of the unpaired electrons in3d- orbitalis promotedgivingtwo pairedelectrons and onevacant3d-orbital. `Ni^(2+)` (Excited state)  (4) Since the coordination number is 4, `Ni^(2+)` gets 4 vacant hybrid orbitalsby hybridisation of one 3d, one 4s and two 4p-orbitals formingfour`dsp^(2)`hybrid orbitals. Thishas square planargeometory. `Ni^(2+)`  (5) 4 lone pairs from `4CN^(-)` ligands are accommodated in the vacantfour `dsp^(-)`hybridorbitals. THUS four `DPS^(2)` hybrid orbitals of `Ni^(2+)`overlap with filledorbitalsof `CN^(-)`forming 4 coordinatebondsgivingsquareplaner gemoeteryto thecomplex. Itis an inner complex. `[Ni(CN)_(4)]^(2-)`  Since the complex ion has all electrons paired, it is diamagnetic. 
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