JEE Chemistry 2024 Question with Solution

Given: The compound is decacarbonyldimanganese(0), written as $\mathrm{Mn_2(CO)_{10}}$.

Find: The coordination geometry around each manganese atom.

From the solution text, the compound is a dimeric metal carbonyl with one $\mathrm{Mn-Mn}$ bond. Each manganese atom is attached to five terminal $\mathrm{CO}$ ligands and one manganese atom.

So, for each manganese center, the coordination number is:

$$5 + 1 = 6$$

A coordination number of $6$ usually corresponds to an octahedral arrangement.

Therefore, the coordination geometry around each manganese atom is octahedral. The correct option is A.

Given: $\mathrm{Mn_2(CO)_{10}}$ is decacarbonyldimanganese(0).

Find: The geometry around manganese.

The detailed solution states that there are $10$ carbonyl ligands for $2$ manganese atoms. In the common structure, the two manganese atoms are connected by one metal-metal bond.

1. Oxidation state of manganese is $0$.
2. Total ligands present are $10\,\mathrm{CO}$ for two metal centers.
3. One coordination site on each manganese is occupied by the $\mathrm{Mn-Mn}$ bond.
4. Each manganese then has five terminal $\mathrm{CO}$ ligands.

Hence each manganese has:

$$\text{coordination number} = 5\,(\mathrm{CO}) + 1\,(\mathrm{Mn-Mn\ bond}) = 6$$

A metal center with coordination number $6$ generally has octahedral geometry.

Therefore, the coordination geometry around manganese is octahedral, so the correct option is A.