In the trans-PtCl2L(CO) complex, the CO stretching frequency for L = NH3, pyridine, NMe3 decreases in the order:a)Pyridine > NH3 > NMe3b)NH3 > Pyridine > NMe3c)NMe3 > NH3 > Pyridined)Pyridine > NMe3 > NH3Correct answer is option 'A'. Can you explain this answer?

Question

In the trans-PtCl2L(CO) complex, the CO stretching frequency for L = NH3, pyridine, NMe3 decreases in the order:a)Pyridine &#62; NH3 &#62; NMe3b)NH3 &#62; Pyridine &#62; NMe3c)NMe3 &#62; NH3 &#62; Pyridined)Pyridine &#62; NMe3 &#62; NH3Correct answer is option 'A'. Can you explain this answer?

Answer

Explanation:

The CO stretching frequency in trans-PtCl2L(CO) complex is affected by the nature of the ligand L. The order of decreasing CO stretching frequency for different ligands is as follows:

a) Pyridine NH3 NMe3

b) NH3 Pyridine NMe3

c) NMe3 NH3 Pyridine

d) Pyridine NMe3 NH3

The reason for this order can be explained by the trans effect of the ligands on the CO molecule.

1. Pyridine has the lowest CO stretching frequency because it has the weakest trans effect on the CO molecule. This is because pyridine is a pi-donor ligand and does not have any lone pair of electrons to donate to the metal center. Therefore, it does not interact strongly with the CO molecule.

2. NH3 has a higher CO stretching frequency than pyridine because it has a stronger trans effect on the CO molecule. This is because NH3 is a stronger sigma-donor ligand and can donate its lone pair of electrons to the metal center. This interaction between the nitrogen lone pair and the metal center weakens the bond between the metal and the CO molecule, resulting in a higher CO stretching frequency.

3. NMe3 has the highest CO stretching frequency because it has the strongest trans effect on the CO molecule. This is because NMe3 is a stronger sigma-donor ligand than NH3 and can donate its lone pair of electrons more effectively to the metal center. This interaction weakens the bond between the metal and the CO molecule even further, resulting in a higher CO stretching frequency.

Therefore, the order of decreasing CO stretching frequency for different ligands in trans-PtCl2L(CO) complex is Pyridine < nh3='' />< nme3.='' />

Answer

More the e donating gr more will be co frq . In case of tert amine steric hind will be more

Answer

I think the answer is c.

when metal atom is connected with electron donating group, M-CO backbonding increases due to large amount of electrons on the metal atom.Hence CO stretching frequency decreases

pyridine is more basic and therefore more electron donating.

Answer

More the electron density or electron donating capacity of ligand lesser the stretching frequency of CO. hence A is correct.

Answer

More the strength of M-C bond , C-O bond gets weaker and stretching frequency of CO decreases
order of trans effect: py> NH3>NMe3
Pt-C bond in case of py us weakest which implies high C-O bond strength and thus high stretching frequency

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