Structure of `Na_(2)[B_(4)O_(5)(OH)_(4)]*SH_(2)O` contains

Options

A. two triangular and two tetrahedral units
B. three triangular and one tetrahedral units
C. all tetrahedral units
D. all triangular units

Answer

To determine the structure of the compound \( \text{Na}_2[\text{B}_4\text{O}_5(\text{OH})_4] \cdot 8\text{H}_2\text{O} \) and identify the number of tetrahedral and trigonal units, we can follow these steps:

### Step 1: Identify the components of the compound
The compound consists of:
- Sodium ions (\( \text{Na}^+ \))
- Boron (\( \text{B} \))
- Oxygen (\( \text{O} \))
- Hydroxyl groups (\( \text{OH} \))
- Water molecules (\( \text{H}_2\text{O} \))

### Step 2: Analyze the boron-oxygen framework
In the structure, boron typically forms tetrahedral geometries due to its ability to form four bonds. The compound has four boron atoms and five oxygen atoms.

### Step 3: Determine the coordination of boron
- Each boron atom can form three bonds with oxygen or hydroxyl groups, leading to a trigonal planar arrangement.
- Additionally, one of the boron atoms can form a tetrahedral unit by bonding to an oxygen atom.

### Step 4: Count the tetrahedral and trigonal units
- From the analysis, we can identify:
- **Tetrahedral units**: There are 2 tetrahedral units formed by the bonding of boron with oxygen.
- **Trigonal units**: There are 2 trigonal units formed by the bonding of boron with three oxygen atoms.

### Step 5: Summarize the findings
Thus, the structure of \( \text{Na}_2[\text{B}_4\text{O}_5(\text{OH})_4] \cdot 8\text{H}_2\text{O} \) contains:
- **2 tetrahedral units**
- **2 trigonal units**

### Final Answer
The structure contains 2 tetrahedral units and 2 trigonal units.

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