Co-Ordination Compounds Question 163
Question: Among the following metal carbonyls, the C-0 bond order is lowest in
Options:
A) $ {{[Mn{{(CO)}_6}]}^{+}} $
B) $ [Fe{{(CO)}_5}] $
C) $ [Cr{{(CO)}_6}] $
D) $ {{[V{{(CO)}_6}]}^{-}} $
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Answer:
Correct Answer: B
Solution:
(1) $ M{n^{+}}=3d^{5}4s^{1}.$ In presence of $ CO, $ effective configuration is $ 3d^{6}4s^{0}.$
$ \Rightarrow $ 3 lone pairs for back bonding with vacant orbital of C in CO. (2) $ Fe^{0}=3d^{6}4s^{2} $ .
In the presence of $ CO $ , effective configuration is $ 3d^{6} $ .
$ \Rightarrow $ 4 lone pairs for back bonding with CO. (3) $ Cr^{0}=3d^{5}4s^{1} $ .
In the presence of CO, effective configuration is $ 3d^{6}.$
$ \Rightarrow $ 3 lone pairs for back bonding with CO.
(4) $ {V^{-}}=3d^{4}4s^{2}.$ In the presence of CO effective configuration is $ 3d^{6}.$
$ \Rightarrow $ 3 lone pairs for back bonding with CO. These maximum back bonding in $ [Fe{{(CO)}_5}] $ , therefore CO bond order is lowest
