The anion of actylacetone (acac) forms `Co(acac)_(3)` chelate with `Co^(3+)` . The rings of the chelate are

Options

A. Three membered
B. Five membered
C. Four membered
D. Six membered

Answer

To determine the number of rings formed in the chelate complex `Co(acac)_(3)`, we need to analyze the structure of the acetylacetonate (acac) ligand and how it coordinates with the cobalt ion.

### Step-by-Step Solution:

1. **Identify the Ligand Structure**:
- The acetylacetonate ion (acac) is derived from acetylacetone, which has the formula CH3C(O)CH2C(O)CH3. The anion form has a negative charge on one of the oxygen atoms.
- The structure can be represented as:
```
O
||
CH3-C-CH2-C-CH3
|
O^-
```
- The acac ligand has two coordination sites, both of which are oxygen atoms.

2. **Determine Coordination with Cobalt**:
- In the complex `Co(acac)_(3)`, cobalt (Co) is in the +3 oxidation state and acts as the central metal ion.
- Each acac ligand coordinates to the cobalt ion through its two oxygen atoms, making it a bidentate ligand.

3. **Calculate the Total Coordination**:
- Since there are three acac ligands coordinating to one cobalt ion, the total number of coordination sites occupied is:
- 3 ligands × 2 coordination sites per ligand = 6 coordination sites.
- This arrangement allows for an octahedral geometry around the cobalt ion.

4. **Identify the Rings Formed**:
- Each acac ligand forms a ring with the cobalt ion. Since each ligand connects through two oxygen atoms, each ligand contributes to the formation of a six-membered ring.
- Therefore, with three acac ligands, we can visualize the structure as having three six-membered rings.

5. **Count the Total Number of Rings**:
- Each of the three acac ligands forms a separate six-membered ring with the cobalt ion.
- Thus, the total number of six-membered rings formed in the complex `Co(acac)_(3)` is **3**.

### Conclusion:
The rings of the chelate formed by the anion of acetylacetone in the complex `Co(acac)_(3)` are **six-membered rings**.