Which of the given compound(s) can act as Lewis acid in both monomer and dimer form?

Options

A. `BH_(3)`
B. `BeCl_(2)`
C. `BeH_(3)`
D. `AlCl_(3)`

Answer

To determine which of the given compounds can act as a Lewis acid in both monomer and dimer forms, we need to analyze each compound based on the definition of a Lewis acid. A Lewis acid is defined as a species that can accept an electron pair due to the presence of vacant orbitals.

### Step-by-Step Solution:

1. **Identify the Compounds**: The compounds given are:
- BS3 (Boron Trisulfide)
- BeCl2 (Beryllium Chloride)
- BeS3 (Beryllium Trisulfide)
- AlCl3 (Aluminum Chloride)

2. **Analyze BS3**:
- **Monomer Form**: BS3 has a boron atom that has vacant p-orbitals. Therefore, it can accept electron pairs, making it a Lewis acid in its monomer form.
- **Dimer Form**: When two BS3 molecules combine, they form B2S6 (diborane), which is also electron-deficient and can accept electron pairs. Thus, BS3 acts as a Lewis acid in both forms.

3. **Analyze BeCl2**:
- **Monomer Form**: BeCl2 has a beryllium atom that can also accept electron pairs due to its vacant orbitals. Hence, it is a Lewis acid in its monomer form.
- **Dimer Form**: When dimerized, BeCl2 forms Be2Cl4, which is also electron-deficient and can accept electron pairs. Therefore, BeCl2 acts as a Lewis acid in both forms.

4. **Analyze BeS3**:
- **Monomer Form**: BeS3 has a beryllium atom that can accept electron pairs, making it a Lewis acid in its monomer form.
- **Dimer Form**: When dimerized, it forms Be2S6, which is also electron-deficient and can accept electron pairs. Thus, BeS3 acts as a Lewis acid in both forms.

5. **Analyze AlCl3**:
- **Monomer Form**: AlCl3 has an aluminum atom with vacant p-orbitals, allowing it to accept electron pairs, making it a Lewis acid in its monomer form.
- **Dimer Form**: When dimerized, AlCl3 forms Al2Cl6, which is also electron-deficient and can accept electron pairs. Therefore, AlCl3 acts as a Lewis acid in both forms.

6. **Conclusion**: All four compounds (BS3, BeCl2, BeS3, and AlCl3) can act as Lewis acids in both their monomer and dimer forms.

### Final Answer:
All of the given compounds (BS3, BeCl2, BeS3, and AlCl3) can act as Lewis acids in both monomer and dimer forms.

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