CO bond length

If CO Bond length = 1.128 Angstorm, then the possible value of CO bond length is Fe(CO) is
(a) 1.128 A
(b) 1.10A
(c) 1.13 A
(d) 10115A
I do not understand how the d pi- p pi bonding will affect eh bond order of CO bond….????

12 Answers

106
Asish Mahapatra ·

d pi- p pi backbonding : the bond order increases (as there is partial extra bond character ) which decreases the bond length. so the bond length of M-CO will be slightly less than CO bond length

So answer is (b)

1
cute_cat ·

can you please explain what is this partial extra bond character?

29
govind ·

The M–C π bond is formed by the
donation of a pair of electrons from a filled d orbital
of metal into the vacant antibonding π* orbital of
carbon monoxide. so due to donation of electrons in antibonding orbital ..bond order decreases so bond length increases

29
govind ·

Actually i think this is a past IIT question..
the answer is definitely 1.13A° ..
well i have seen somewhere it was given as a multiple correct question ..and there one of the options given was 1.70 and it was correct..the reason given was that due to addition of electrons in the antibonding orbitals the bond length will increase...but i dont think it will increase this much..
Please someone confirm it...

1
Great Dreams ·

yes its syngeric bonding in metal complexes
refer ncert where it is explained clearly

1
Great Dreams ·

this image should help

29
govind ·

@Tom...
Ya i know all abt this...I just want to confirm whether the bond length will increase from 1.128A to 1.70A in case of synergic bonding??...

1
Great Dreams ·

yes the bond length increases

29
govind ·

@Tom...arrey yaar u r not getting my point...in JD Lee it's written that bond length increases from 1.128A to 1.15A..and my dbt is will the bond length increase upto 1.70A due to synergic bonding?

39
Pritish Chakraborty ·

Well what I've studied about bonding in metal carbonyls...the bond length increase happening due to synergic effect is because the bond order of C - O is reduced from triple to double bond. Thus bond length increases to 1.5 A in many carbonyls...nowhere did I see an example of 1.70 A..thats a bit too much I think.

29
govind ·

@Pritish where have u studied that it increases upto 1.5A ..i guess that figure shud be 1.15A..that's wat JD Lee says..anyways thanks for the reply..

39
Pritish Chakraborty ·

yeah sorry 1.15 A lol typo.

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