Ferrocene is

Options

A. `Fe(eta^(5) - C_5H_5)_2`
B. `Fe(eta^(2) - C_5H_5)_2`
C. `Cr(eta^(2) - C_5H_5)_5`
D. `Os(eta^(5) - C_5H_5)_2`

Answer

**Step-by-Step Solution:**

1. **Understanding Ferrocene:**
Ferrocene is an organometallic compound consisting of iron sandwiched between two cyclopentadienyl (Cp) rings. The chemical formula for ferrocene is \( \text{C}_5\text{H}_5\text{FeC}_5\text{H}_5 \) or simply \( \text{Fe}(\text{C}_5\text{H}_5)_2 \).

2. **Identifying the Structure:**
In ferrocene, the iron (Fe) atom is coordinated with two cyclopentadienyl rings. Each cyclopentadienyl ring is a five-membered carbon ring with a negative charge, which allows it to coordinate with the iron atom.

3. **Coordination Number (η):**
The term "η" (eta) refers to the number of atoms in a ligand that are bonded to the central metal atom. In the case of ferrocene, each cyclopentadienyl ring coordinates with the iron through all five carbon atoms. Therefore, it is referred to as η⁵ (eta five).

4. **Conclusion:**
Given the options provided, the correct identification of ferrocene is the one that shows two η⁵ cyclopentadienyl rings coordinated to an iron atom. This structure is crucial for understanding the bonding and stability of ferrocene.

5. **Final Answer:**
The correct answer is the option that depicts ferrocene as having two η⁵ cyclopentadienyl rings coordinated to iron.

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