Question

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

• A. Total number of valence shell electrons at metal centre in $Fe(CO{)}_5$ or $Ni(CO{)}_4$ 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) Electronic configuration of central metal atom in both cases is $\left[Ar\right]3d^{10}4s^{2}4p^6$ (8 electrons in outermost shell and 18 valence electrons respectively).
(b) Low spin complex because CO is a strong field ligand.
(c) Metal-carbon bond strengthens when the oxidation state of metal is lowered.
(d) The carbonyl C - O bond becomes stronger when the oxidation state is increased.