Which of the following is a chelate complex ion?

Options

A. `[Cu(en)_(2)]^(2+)`
B. `[CuCI_(4)]^(2-)`
C. `[Cu(NH_(3))_(4)]^(2-)`
D. `[Cu(CN)_(4)]^(3-)`

Answer

To determine which of the given options is a chelate complex ion, we need to analyze the ligands associated with each complex and identify if any of them can form a cyclic structure around the central metal ion.

### Step-by-Step Solution:

1. **Understanding Chelate Complexes**:
- A chelate complex is formed when a ligand binds to a central metal atom in such a way that it creates a ring structure. This typically occurs with bidentate or polydentate ligands, which have multiple donor atoms that can coordinate to the metal.

2. **Analyzing the Given Options**:
- **Option 1: CuEn2 2+**
- Here, "En" stands for ethylenediamine (NH2CH2CH2NH2), which is a bidentate ligand. It has two nitrogen atoms that can donate lone pairs to the copper ion (Cu). This ligand can wrap around the copper ion, forming a cyclic structure.
- **Option 2: CuCl4**
- Chloride ions (Cl-) are monodentate ligands, meaning they can only attach to the metal at one point. Therefore, they cannot form a cyclic structure.
- **Option 3: Cu(NH3)4**
- Ammonia (NH3) is also a monodentate ligand. Although it can coordinate to the metal, it cannot form a cyclic structure due to its single donor atom.
- **Option 4: CuCN4 3-**
- Cyanide (CN-) is another monodentate ligand. Like the previous examples, it cannot form a cyclic structure with the metal.

3. **Conclusion**:
- Among the given options, only **CuEn2 2+** can form a chelate complex due to the presence of the bidentate ligand ethylenediamine, which allows it to create a cyclic structure around the copper ion.

### Final Answer:
**CuEn2 2+** is a chelate complex ion.