Which of the following statements is correct with respect to the metal carbonyls of `I^(st)` transition series?

Options

A. As M - `Cpi` bonding increases , the C-O bond becomes weaker
B. As positive charge on the central metal atom increases , the C-O bond becomes weaker
C. As electron density on the central metal atom increases, the C-O bond becomes weaker
D. (A) and (C ) both

Answer

D

Explanation

Order of C-O bond strength, `[Mn(CO)_6]^(+) gt [Cr(CO)_6]gt [V(CO)_6]^(-)gt [Ti(CO)_6]^(2-) gt and [Ni(CO)_4] gt [Co(CO)_4]^(-) gt [Fe(CO)_4]^(2-)`.
(A)True statement.
(B)As + ve charge on the central metal atom increases, the less readily the metal can donate electron density into the `pi^(**)` orbitals of CO ligand to weaken the C-O bond.
(C )In the carbonylate anions, the metal has a greater electron density to be dispersed, with the result that M-`Cpi` bonding is enhanced and the C-O bond is diminished in strength.