Question

The correct statement(s) regarding the binary transition metal carbonyl compounds is (are)
(Atomic numbers: Fe - 26, Ni - 28)

• A. Total number of valence shell electrons at metal centre in $Fe\left(CO{)}_{5}orNi\right(CO{)}_4$ is 16
• B. These are predominantly low spin in nature
• C. Metal - carbon bond strengthens when the oxidation state of the metal is lowered
• D. The carbonyl C - O bond weakens when the oxidation state of the metal is increased

Answer 1

Answer: (B), (C)

Metal - carbon bond strengthens when the oxidation state of the metal is lowered

(A) $\left[Fe\right(C{O}_5\left)\right]\text{\&}\left[Ni\right(CO{)}_4]$ complexes have 18-electrons in their valence shell.

(B) Carbonyl complexes are predominantly low spin complexes due to strong ligand field.

(C) As electron density increases on metals (with lowering oxidation state on metals), the extent of synergic bonding increases. Hence M-C bond strength increases.

(D) While positive charge on metals increases and the extent of synergic bond decreases and hence C - O bond becomes stronger.