Which of the following complex is not a chelate?

Question

Accepted Answer

Option 3, Tetraamine dichlorocobalt (III) nitrate, is the correct answer because it is not a chelate complex. To understand why this is the case, let's first define what a chelate is. A chelate is a complex in which a ligand forms multiple bonds to a single central metal atom, creating a ring structure. Chelating ligands are typically bidentate or polydentate, meaning they have two or more donor atoms that can simultaneously coordinate to the metal center.

Now, let's examine each option:

1. **bis (dimethylglyoximato) nickel (II):** This complex is a chelate because dimethylglyoxime is a bidentate ligand. It has two donor atoms that can coordinate with the nickel ion, forming a stable ring structure.

2. **Potassium ethylenediaminetetrathiocyanato chromate (III):** This complex is also a chelate. Ethylenediamine is a well-known bidentate ligand, meaning it can form two bonds with the central metal atom, creating a ring structure. The presence of thiocyanate ions does not change the chelating nature of ethylenediamine.

3. **Tetraamine dichlorocobalt (III) nitrate:** This complex is not a chelate because it involves monodentate ligands. Ammonia (NH3) is a monodentate ligand, meaning it can only form one bond with the central metal atom. Similarly, chloride ions are also monodentate. Since there are no bidentate or polydentate ligands forming ring structures with the cobalt ion, this complex does not qualify as a chelate.

4. **Trans diglycenatoplatinum (II):** This complex is a chelate because glycinate is a bidentate ligand. It can coordinate with the platinum ion through both the nitrogen and oxygen atoms, forming a ring structure.

In summary, Option 3, Tetraamine dichlorocobalt (III) nitrate, is not a chelate because it consists of only monodentate ligands, which do not form the ring structures characteristic of chelate complexes.