In which one of the following metal carbonyls, CO forms a bridge between metal atoms?

Question: In which metal carbonyl does CO form a bridge between metal atoms?

Analyse each metal carbonyl.

$$[Co_2(CO)_8]$$ (Option 1): Dicobalt octacarbonyl exists in two isomeric forms. One isomer has two bridging CO groups connecting the two Co atoms (along with six terminal CO groups), and the other has a direct Co-Co bond with all terminal COs. The bridged form is well-known and commonly depicted in textbooks. This compound does have bridging CO.

$$[Mn_2(CO)_{10}]$$ (Option 2): This has a direct Mn-Mn bond with all ten CO groups in terminal positions. No bridging CO.

$$[Os_3(CO)_{12}]$$ (Option 3): This has a triangular Os₃ framework with all twelve CO groups in terminal positions (four per Os atom). No bridging CO.

$$[Ru_3(CO)_{12}]$$ (Option 4): Similar to the osmium analogue, this has all terminal CO groups. No bridging CO.

The correct answer is Option 1: $$[Co_2(CO)_8]$$.