Red precipitae is obtained when ethanol solution of dimethylglyoxime is added to ammoniacal `Ni (II)`. Which of the following statement is not true?

Options

A. Red complex has a square planar geometry
B. Complex has symmetrical H-bonding
C. Red complex has a tetrahedral geometry
D. Dimethylglyoxime functions as bidentate ligand

Answer

To solve the question, we need to analyze the statements provided and determine which one is not true based on the information given about the red precipitate formed when dimethylglyoxime (DMG) is added to ammoniacal Ni(II).

### Step-by-Step Solution:

1. **Understanding the Reaction**:
- When an ethanol solution of dimethylglyoxime is added to ammoniacal Ni(II), a red precipitate is formed. This indicates the formation of a complex between Ni(II) and dimethylglyoxime.

2. **Identifying Dimethylglyoxime (DMG)**:
- The structure of dimethylglyoxime can be represented as CH3-C(=N-OH)-C(=N-OH)-CH3. It has two nitrogen atoms that can donate lone pairs to form coordinate bonds with metal ions.

3. **Determining the Ligand Behavior**:
- Since dimethylglyoxime has two donor sites (the nitrogen atoms), it acts as a bidentate ligand. This confirms that statement D is true.

4. **Formation of the Complex**:
- The complex formed is Ni(DMG)2. Each DMG molecule loses a hydrogen ion (H⁺) when it coordinates with Ni(II), resulting in a net charge of zero for the complex.

5. **Analyzing the Geometry**:
- Nickel in the +2 oxidation state has the electron configuration of [Ar] 3d⁸. When it forms a complex with a strong field ligand like DMG, the electrons will pair up, allowing for hybridization.
- The hybridization of Ni in this complex is dsp², which corresponds to a square planar geometry. Thus, statement A is true.

6. **Evaluating Hydrogen Bonding**:
- The complex exhibits intramolecular hydrogen bonding due to the presence of hydroxyl groups in DMG. Therefore, statement B is also true.

7. **Identifying the False Statement**:
- Statement C claims that the red complex has a tetrahedral geometry. However, we have established that the geometry is square planar (due to dsp² hybridization), making statement C false.

### Conclusion:
The statement that is not true is option C: "red complex has a tetrahedral geometry."