Much like the CO ligands, cyanide (CN-) ligands have IR stretching frequencies that are distinctive and...

Much like the CO ligands, cyanide (CN^-) ligands have IR stretching frequencies that are distinctive and therefore often particularly useful. Consult an appropriate character table, and give a reducible representation for the cyanide stretching vibrations in the square-planar tetracyanoplatinate(II) ion, Pt(CN)₄^2-.

Expert Solution

Answer :

CN- is isoelectronic with CO and NO+. Both CO and CN- co-ordinate to the metal atom through carbon. The free CN- ion has a stretching frequency of 2080 cm-1, in complexes it generally has a higher value and a sharp absorption in the range 2000-2200 cm-1 is observed.

In the free state the contribution of II a is greater than I a towards the resonance hybrid.
In complexes the contribution of I b or II b depends on the metal atom to which it is coordinated. It has been found that CN stretching frequency in its complexes depends on electro negativity, oxidation state and co-ordination number of the metal atom.

Electro negativity of the metal The stretching frequency of the ligand CN increases with increase in electro negativity of the metal ion.

[ Ni (CN)4]2- < [ Pd (CN)4]2- < [ Pt (CN)4 ]2-

2135 cm-1 2143 cm-1 2150 cm-1

In the graph the CN- strching frequncy is in 2135 cm-1

queen_honey_blossom answered 10 months ago

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