Why the CO stretching frequency of metal complexes V(CO)-1, Cr(CO)6 and Mn(CO) 6 +1 are reduced from the expected value ?
All the
three given metal carbonyl complexes are
iso electronic and hexa coordinated . Thus iso electronic complexes forming
metal species are V -1 , Cr0 and Mn +1
respectively .
Each complex
is octahedral in shape and the ligand CO is a π-acid ligand.In each case there is
bonding and back-bonding takes place between the metal and the ligand .
Since each
complex species is a d 6- system ,therefore there is a possibility
of formation of such π-bonding with three CO groups at a time in each case and by resonance each
M-CO bond occupy some multiple bond
character .
By
calculation it can be found that each M – C bond order 1.6 . During back-bonding the back-donated
electron pairs from metal is taken up by C-atom of CO ligand in its vacant π*orbital, as a result the bond order of CO molecule in the
complex is reduced to some extent from the real value of 3 which is found in
free CO molecules.
Thus stretching
frequency is reduced in complex from the
value of 2143 cm -1 , which is necessary for free CO molecule.
The more the
degree of back-bonding the more is the lowering in such frequency . In the
complexes V(CO)6 -1, Cr(CO)6 and Mn(CO) 6 +1
the metal ions are are V -1 ,Cr0 and Mn +1
respectively .
Back bonding
ability of metal ion depends on its oxidation state and it is clear that
ability decreases in the order of V -1 > Cr0 > Mn +1.
For the
above reason the CO stretching frequency
of metal complexes V(CO)6 -1, Cr(CO)6 and Mn(CO) 6
+1 are reduced from the expected value .
Practice problem:
Why the CO stretching frequency of metal complexes V(CO)6 -1, Cr(CO)6 and Mn(CO) 6 +1 are reduced from the expected value ?
Why the CO stretching frequency of metal complexes V(CO)6 -1 is less than expected value ?
Why the CO stretching frequency of metal complexes Cr(CO)6 is less than expected value ?
Now day, everything is going to find a new but well settled and successful stream for their career. When I came to this blog, I really impressed by all the knowledge points mentioned here. Thank you for this assistance.Boron Nitride Crucible
ReplyDelete