Structure of Os5(CO)16

The correct answer for the structure of Os5(CO)16 is option 'B', which represents the closo structure. Let's understand this structure and the other options in detail.

a) Nido Structure:
The nido structure is a term used for cluster compounds where the central atom is bonded to a vertex of the cluster. In the nido structure, the central atom is not fully encapsulated by the surrounding ligands. However, in the case of Os5(CO)16, the Os atom is fully encapsulated by the CO ligands, so it does not adopt the nido structure.

b) Closo Structure:
The closo structure is a term used for cluster compounds where the central atom is fully encapsulated by the surrounding ligands. In the closo structure of Os5(CO)16, the Os atom is surrounded by a cluster of 5 CO ligands, forming a closed cage-like structure. This is the correct structure for Os5(CO)16.

c) Arachno Structure:
The arachno structure is a term used for cluster compounds where the central atom is bonded to some of the vertices of the cluster, but not all. In the arachno structure, the central atom is partially encapsulated by the surrounding ligands. However, in the case of Os5(CO)16, the Os atom is fully encapsulated by the CO ligands, so it does not adopt the arachno structure.

d) Hypo Structure:
The hypo structure is a term used for cluster compounds where the central atom is bonded to only one vertex of the cluster. In the hypo structure, the central atom is minimally encapsulated by the surrounding ligands. However, in the case of Os5(CO)16, the Os atom is fully encapsulated by the CO ligands, so it does not adopt the hypo structure.

Summary:
In summary, the correct structure for Os5(CO)16 is the closo structure. The Os atom is fully encapsulated by the surrounding CO ligands, forming a closed cage-like structure. The other options, such as nido, arachno, and hypo structures, are not applicable in this case as they involve partial encapsulation or bonding to fewer vertices of the cluster.