Question

The correct statement(s) regarding Co\(_2\)(CO)\(_8\) is(are)

• A. It reacts with Na to give Na[Co(CO)\(_4\)]
• B. It contains three bridging carbonyls
• C. It can be prepared by reductive carbonylation of Co(OAc)\(_2\)\(\cdot\)4H\(_2\)O
• D. Two isomers exist in hexane solution

Hint:

Remember: Co\(_2\)(CO)\(_8\) \(\leftrightharpoons\) bridged (2 \(\mu-CO)\) and unbridged (all terminal) isomers.
Alkali metals convert many metal carbonyl dimers to anionic monocarbonylates, e.g., Na[Co(CO)\(_4\)].

Answer 1

The Correct Option is A, C, D

Step 1: Reduction with alkali metals. Co\(_2\)(CO)\(_8\) is reduced by Na to give the cobaltate carbonyl anion: \[ \mathrm{Co_2(CO)_8 + 2\,Na \rightarrow 2\,Na[Co(CO)_4],} \] so (A) is true.
Step 2: Carbonyl structure. One isomer of Co\(_2\)(CO)\(_8\) has two bridging CO ligands (not three); the other isomer has all terminal CO ligands. Therefore (B) is false.
Step 3: Preparation. Co\(_2\)(CO)\(_8\) is prepared by reductive carbonylation of cobalt(II) salts (e.g., cobalt acetate) under CO pressure \(\Rightarrow\) (C) true.
Step 4: Isomerism in solution. In nonpolar solvents like hexane, Co\(_2\)(CO)\(_8\) exists as an equilibrium mixture of the bridged and unbridged isomers \(\Rightarrow\) (D) true.