What will the structure of `CrO_(5)` in presence of pyridine ?

Options

A. Butterfly
B. Square pyramidal
C. Pentagonal pyramidal
D. Cannot be predicted

Answer

To determine the structure of CrO₅ in the presence of pyridine, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Composition of CrO₅**:
CrO₅ consists of chromium (Cr) and five oxygen (O) atoms. Among these, four oxygen atoms are linked through peroxide (O-O) linkages, and one oxygen is doubly bonded to chromium.

**Hint**: Recall the bonding nature of CrO₅ and the role of peroxide linkages.

2. **Identify the Role of Pyridine**:
Pyridine (C₅H₅N) acts as a ligand, donating its lone pair of electrons to form a complex with CrO₅. This results in the formation of a new complex, CrO₅·Py.

**Hint**: Remember that ligands can change the geometry of a metal complex by coordinating to the metal center.

3. **Determine the Coordination Number**:
In the complex CrO₅·Py, the chromium atom is coordinated by six ligands: four from the peroxide oxygens, one from the doubly bonded oxygen, and one from the pyridine.

**Hint**: Count the number of ligands attached to the central metal atom to determine the coordination number.

4. **Predict the Geometry Based on Coordination Number**:
With a coordination number of six, the most common geometries are octahedral and pentagonal pyramidal. However, since we have a specific arrangement with five ligands forming a base and one ligand above the base, the geometry is pentagonal pyramidal.

**Hint**: Visualize how the ligands are arranged around the metal center to determine the shape.

5. **Evaluate the Options**:
- Option 1: Butterfly – This is the structure of CrO₅ alone, not in the presence of pyridine.
- Option 2: Square pyramidal – This is incorrect as it only accounts for five ligands.
- Option 3: Pentagonal pyramidal – This matches our prediction based on the coordination number and geometry.
- Option 4: Cannot be predicted – This is incorrect as we have determined the structure.

**Hint**: Compare the predicted structure with the given options to choose the correct one.

### Final Answer:
The structure of CrO₅ in the presence of pyridine is **pentagonal pyramidal** (Option 3).

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