Chemical Forums

Please login or register.

Login with username, password and session length

Sponsored links

Pages: [1]   Go Down

Author Topic: vibrational frequency CO blue shift (M-CO)  (Read 465 times)

0 Members and 1 Guest are viewing this topic.

xshadow

  • Regular Member
  • ***
  • Mole Snacks: +0/-0
  • Offline Offline
  • Posts: 97
vibrational frequency CO blue shift (M-CO)
« on: June 29, 2017, 03:51:07 AM »

Hi!!

I don't understand why in some complex like M-CO (where M= K+,Na+,Cs+.Rh+)  the stretching frequency of the CO bond  INCREASES (blue shift)


In this complex there is a sigma donation,from the HUMO of CO to the metal  (no backdonation,no "d" electrons).
How can sigma donation increase the freqeuncy  (i.e. the strenght  of this bond)  ??

CO """loses""" some electrons when acts like a sigma donator ,so the CO bond shouldn't be less strong?)


Thanks!! :)
Logged

xshadow

  • Regular Member
  • ***
  • Mole Snacks: +0/-0
  • Offline Offline
  • Posts: 97
Re: vibrational frequency CO blue shift (M-CO)
« Reply #1 on: July 15, 2017, 11:27:27 PM »

No  one??

I don't understand this blue shift of CO
Logged

xshadow

  • Regular Member
  • ***
  • Mole Snacks: +0/-0
  • Offline Offline
  • Posts: 97
Blue Shift CO stretching in M-CO
« Reply #2 on: July 15, 2017, 11:35:35 PM »

Someone can explain me why there is a blue shift when CO interacts with M (where M=Na+,Li+,K+,Cs+)

I know that there is sigma donation from the HOMO of CO to "M" center.


Now if there is a blue shift it means  that the CO bond becomes stronger than before...BUT how this can be possible?
(a sigma donation from CO towards another species...how can this increase the CO bond strenght)

Please help me!!
Thanks.
Logged

Corribus

  • Chemist
  • Sr. Member
  • *
  • Mole Snacks: +366/-20
  • Offline Offline
  • Gender: Male
  • Posts: 2306
  • A lover of spectroscopy and chocolate.
Re: vibrational frequency CO blue shift (M-CO)
« Reply #3 on: July 16, 2017, 04:34:30 AM »

Perhaps not exactly what you are looking for, but similar enough.

https://en.wikipedia.org/wiki/Pi_backbonding
Logged
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?  - Richard P. Feynman

xshadow

  • Regular Member
  • ***
  • Mole Snacks: +0/-0
  • Offline Offline
  • Posts: 97
Re: vibrational frequency CO blue shift (M-CO)
« Reply #4 on: July 16, 2017, 04:45:42 AM »

Perhaps not exactly what you are looking for, but similar enough.

https://en.wikipedia.org/wiki/Pi_backbonding

In that I case I understand why...The metal send some electron density towards an antibond orbital thanks the backdonation
So it is clear that the CO bond becomes weaker...


But here is different...the CO   makes a sigma donation from its HOMO( a non-bonding orbital with a very little bonding character)  to the empty "metal" orbital.

How can this creates the opposite situation? I.e. a CO bond weaker??
Logged

Corribus

  • Chemist
  • Sr. Member
  • *
  • Mole Snacks: +366/-20
  • Offline Offline
  • Gender: Male
  • Posts: 2306
  • A lover of spectroscopy and chocolate.
Re: vibrational frequency CO blue shift (M-CO)
« Reply #5 on: July 17, 2017, 05:17:24 AM »

Maybe it would be helpful if you would provide some actual data for me to look at, then we can work through it.
There are plenty of places that discuss CO ligand interactions with metals:

e.g. (first hit through google)

https://organometallicchem.wordpress.com/2012/01/17/epic-ligand-survey-carbon-monoxide/

But you seem to have a very specific question that's framed in a very vague way.
Logged
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?  - Richard P. Feynman
Pages: [1]   Go Up
 

Mitch Andre Garcia's Chemical Forums 2003-Present.

Page created in 0.055 seconds with 23 queries.