The organic species isolobal to $\left[\mathrm{Fe}(\mathrm{CO})_{2}\left(\mathrm{PPh}_{3}\right)\right]^{-}$is
(a)$\mathrm{CH_2^{+}}$
(b)$\mathrm{CH^{-}}$
(c)$\mathrm{CH_3}$
(d)$\mathrm{CH}$
Answer
Answer (as printed): D
Explanation
$\mathrm{Fe(-1)}\rightarrow d^{9}$ system$d^{9}$ $\mathrm{ML_3}$ CHFor $d^{9}$–$\mathrm{ML_3}$, original co-ordination number will be considered as $\mathrm{ML_6}$.Therefore, $[\mathrm{Fe(CO)_2(PPh_3)}]^{-}$ having three co-ordination number, missing three from original $\mathrm{ML_6}$ and similarly for CH, three ligands also missing from original $\mathrm{CH_4}$.Hence, $[\mathrm{Fe(CO)_2(PPh_3)}]^{-}$ is isolobal with CH but not with $\mathrm{CH_2^{+}}$ $(5e^{-})$ because two ligands missing from original $\mathrm{CH_4}$.