${\mathrm{Co}}_2(\mathrm{CO}{)}_8$ is known as dicobalt octacarbonyl. Here each $\mathrm{Co}$ atom is surrounded by $3 \mathrm{CO}$ ligands termial and $2 \mathrm{CO}$ ligand bridges. It has one metal-metal bond. Therefore its structure is:

${\mathrm{Fe}}_3{\left(\mathrm{CO}\right)}_{12}$ is triiron dodecacarbonyl. It has two $\mathrm{CO}$ ligand bridges as shown below.

${\mathrm{Mn}}_2{\left(\mathrm{CO}\right)}_{10}$ is dimanganese decacarbonyl. It contain no ligand bridges as shown below.

${\mathrm{Fe}}_2{\left(\mathrm{CO}\right)}_9$ contain three $\mathrm{CO}$ bridges as shown below.