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Physical Chemistry

Blazing goIITian

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12 Apr 2008 19:06:19 IST

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501

BOND ORDER QUES

None

Among the following metal carbonyls , the C-O bond order is lowest in

a) [Mn(CO)₆]⁺ b)[Fe(CO)₅]

c) [Cr(CO)₆] d) [V(CO)₆]^-

Please explain with proper reasoning

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Comments (7)

pratik Agarwal

Blazing goIITian

Joined: 23 Jan 2008

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12 Apr 2008 19:27:35 IST

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it is d

Priyesh

Blazing goIITian

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12 Apr 2008 19:41:01 IST

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nopes ans given is b)

joy francis

Blazing goIITian

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12 Apr 2008 21:06:41 IST

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Nahi yaar..i remeber this is a very controversial questions from last year..dekh

CO whenever makes a complex...it accepts electrons it it's antibonding orbitals

resulting in a decrease in BO..now tendency to accept these electrons become less as the charge on the cation increases and vice versa..toh V pe negitive charge kee wajeh se the bond order is least in (d)..

Priyesh

Blazing goIITian

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12 Apr 2008 22:20:41 IST

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nopes all major institutes have given the answer as b)

Brad

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12 Apr 2008 22:34:42 IST

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Mn⁺ ---> 3d 5 4s1 now when CO is present, effective configuration = 3d 6 4s 0

So 3 lone pairs for back bonding with vacant orbital of C in CO

Fe ---> 3d6 4s2 in presence of CO , eff config = 3d 8 i,e 4 lone pairs for back bonding

Cr ----> 3d5 4s1 effective config = 3d 6

so 3 lone pairs for back bonding

V ^- ---> 3d 4 4s2 so eff. config = 3d 6 ; again 3 lone pairs for back bonding

Thus max back bonding in Fe(CO)₅.

So CO bond order lowest.

Priyesh

Blazing goIITian

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17 Apr 2008 17:56:17 IST

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exactly same solution is written in my book but i cant get it can u explain how four lone pairs are available for back bonding in Fe
and 3 in others

aNdRoMeDa

Blazing goIITian

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19 Apr 2008 02:20:44 IST

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fe has 8 elctrons means 4 pairs of elctrons means 4 lone pair of elctrons

similarly othrs hav 6 elctrons means 3 lone pairs

hope u get it

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