Question

Which of the following has the longest \[C - O\] bond length? (Free \[C - O\] bond length in \[CO\] is\[{1.128^ \circ }A\])
A. \[Ni{(CO)_4}\]
B. \[{[Co{(CO)_4}]^8}\]
C. \[{[Fe{(CO)_4}]^{2 - }}\]
D. \[{[Mn{(CO)_6}]^ + }\]

Answer 1

Hint: The higher the oxidation state of the central metal atom, the shorter will be the bond length of \[C - O\] bond as the bond will be strong. The \[C - O\] bond is firmly captivated towards oxygen. Bond lengths for paraffinic \[C - O\] bonds are in the scope of 143 pm – not exactly those of C–N or C–C bonds. The \[C - O\] bond quality is additionally bigger than C–N or C–C. For instance, bond qualities are 91 kilocalories \[\left( {380{\text{ }}kJ} \right)/mol\] (at 298 K) in methanol, 87 kilocalories \[\left( {360{\text{ }}kJ} \right)/mol\] in methylamine, and 88 kilocalories \[\left( {370{\text{ }}kJ} \right)/mol\] in ethane.

Step by step answer: According to our question, correct answer is \[{[Fe{(CO)_4}]^{2 - }}\]as it has longest \[C - O\] bond length among the given complexes. In its typical expression, the \[C - O\] bond length is simply \[1.43\dot A\], when present in oxatriquinane in any case, the bond length (otherwise called bond separation) is normally extended to \[1.54\dot A\]. Bond length is the normal separation between the cores of two ions that are reinforced together in a solitary atom.
In \[Ni{(CO)_4}\]​⇒ Oxidation state of \[Ni\] = 0
In \[{[Co{(CO)_4}]^8}\] ⇒ Oxidation state of \[Co\]= 0
In \[{[Fe{(CO)_4}]^{2 - }}\] ⇒ Oxidation state of \[Fe\] = −2
In \[{[Mn{(CO)_6}]^ + }\] ⇒ Oxidation state of \[Mn\] = +1
The order of bond length of the given complexes is: \[{[Mn{(CO)_6}]^ + } < Ni{(CO)_4} < {[Co{(CO)_4}]^8} < {[Fe{(CO)_4}]^{2 - }}\]

Hence the correct option is (C).

Note: Due to back bonding between metal-carbon bonds, the length of \[C - O\] increases. So bond length is higher. Carbon monoxide (CO) is a lackluster, unscented, and boring combustible gas that is marginally less thick than air. It is harmful to creatures that utilization hemoglobin as an oxygen transporter (both invertebrate and vertebrate) when experienced in focuses above around 35 ppm, in spite of the fact that it is additionally delivered in typical creature digestion in low amounts, and is thought to have some ordinary organic capacities. In the environment, it is spatially factor and fleeting, having a function in the arrangement of ground-level ozone.