In the complex, $\left[\mathrm{Ni}_{2}\left(\eta^{5}-\mathrm{Cp}\right)_{2}(\mathrm{CO})_{2}\right]$, the IR stretching frequency appears at $1857 \mathrm{cm}^{-1}$ (strong) and 1897 $\mathrm{cm}^{-1}$ (weak). The valence electron count and the nature of the M-CO bond respectively are
(a)16 e-, bridging
(b)$17 \mathrm{e}-$, bridging
(c)18 e-, terminal
(d)$18 \mathrm{e}-$, briding
Answer
Answer: D ✓ checked by 4AB · confidence high
The source book printed C; on checking, D is correct — see the explanation.
Explanation
[CpNi(CO)]₂: each Ni has 10 + 5 (Cp) + 2 (bridging CO) + 1 (Ni–Ni) = 18 electrons, and the low CO stretches (1857/1897 cm⁻¹) show bridging carbonyls (d).