In the cluster $\left[\mathrm{Co}_{3}(\mathrm{CH})(\mathrm{CO})_{9}\right]$ obeying 18e rule, the number of metal-metal bonds and the bridging ligands respectively, are
(a)3 and 1 CH
(b)0 and 3 CO
(c)3 and 1 CO
(d)6 and 1 CH
Answer
Answer: A ✓ checked by 4AB · confidence high
Explanation
[Co₃(μ₃-CH)(CO)₉] has a Co₃ triangle (3 Co–Co bonds) capped by one μ₃-CH; all nine CO are terminal. Each Co reaches 18 e (a).