According to Wade's rules, the correct structural types of $\left[\mathrm{Co}\left(\eta^{5}-\mathrm{C}_{5} \mathrm{H}_{5}\right) \mathrm{B}_{4} \mathrm{H}_{8}\right]$ and $\left[\mathrm{Mn}\left(\eta^{2}-\mathrm{B}_{3} \mathrm{H}_{8}\right)(\mathrm{CO})_{4}\right]$ are
(a)closo and nido
(b)nido and arachno
(c)closo and arachno
(d)nido and nido
Answer
Answer: B ✓ checked by 4AB · confidence high
Explanation
[CpCoB₄H₈]: CpCo gives 2 e, four BH 8 e, four extra H 4 e = 14 = 2n + 4 for five vertices → nido. [Mn(η²-B₃H₈)(CO)₄]: Mn(CO)₄ 3 e + B₃H₈ 11 e = 14 = 2n + 6 for four vertices → arachno.