Question

Give the formula of a complex constructed from one \(\mathrm{Ni}^{2+}\) ion, one ethylenediamine ligand, three ammonia molecules, and one water molecule. Is the complex neutral or is it charged? If charged, give the charge.

Short answer

The complex formula is \([\text{Ni(en)(NH}_3\text{)}_3\text{(H}_2\text{O)]}^{2+}\) and it has a charge of +2.

Step-by-step solution

Understanding the components

To solve this problem, we must first identify all the components involved in the complex. The components listed are: one \(\mathrm{Ni}^{2+}\) ion, an ethylenediamine ligand (often abbreviated as \(\text{en}\)), three ammonia (\(\mathrm{NH}_3\)) molecules, and one water (\(\mathrm{H}_2\mathrm{O}\)) molecule. It's important to know that ethylenediamine is a bidentate ligand, meaning it can attach to the metal center at two points.

Assigning charges to the ligands and metal ion

The \(\mathrm{Ni}^{2+}\) ion has a charge of \(+2\). Ammonia and water are neutral ligands and have no charge contribution. Ethylenediamine is also neutral. Therefore, only the metal center contributes to the charge of the complex.

Construct the formula of the complex

Now, we can write the formula of the complex using the information about the components: \(\text{[Ni(en)(NH}_3\text{)}_3\text{(H}_2\text{O)]}^{2+}\). The complex incorporates one \(\mathrm{Ni}^{2+}\) ion, one ethylenediamine ligand, three ammonia molecules, and one water molecule.

Determine the overall charge of the complex

Since ethylenediamine, ammonia, and water are all neutral in terms of charge, they do not affect the overall charge of the complex. Therefore, the overall charge of the complex is simply the charge of the \(\mathrm{Ni}^{2+}\), which is \(+2\). Thus, the complex is charged: \([\text{Ni(en)(NH}_3\text{)}_3\text{(H}_2\text{O)]}^{2+}\).

Key concepts

Complex Ions

Complex ions form when a central metal ion binds ligands around it, creating a more stabilized and often colorful assembly. These complexes are prevalent in coordination chemistry. For example, in our exercise, a nickel ion (\(\text{Ni}^{2+}\)) acts as the central metal cation. It coordinates with various molecules to form a stable structure.

Key points about complex ions involve:

• Central Metal Ion: It typically possesses a positive charge facilitating attraction with ligands.
• Ligands: Molecules or ions that donate electron pairs to the metal.
• Coordination Number: The total number of ligand bonds to the metal ion, influencing the complex's geometry.

Complex ions are essential in understanding the bonding and properties of coordination compounds.

Ligands

Ligands are crucial in the structure of complex ions, serving as electron pair donors to attach to a central metal ion. In the context of coordination chemistry, ligands can be classified based on the number of donor sites they possess. The most common types include:

• Monodentate Ligands: Attach to the metal through a single donor atom. Examples are ammonia (\(\text{NH}_3\)) and water (\(\text{H}_2\text{O}\)).
• Bidentate Ligands: Use two donor atoms to bind at two sites. Ethylenediamine (\(\text{en}\)) is a typical example.
• Polydentate Ligands: Bind through multiple sites, stabilizing the complex even further.

Understanding ligands helps predict how they impact the stability and reactivity of complex ions. In our example, ethylenediamine as a bidentate ligand enhances the robustness of the nickel complex.

Coordination Compounds

Coordination compounds encompass complex ions surrounded by ligands and possibly additional counter ions to maintain electrical neutrality. These compounds are integral in various applications, from industrial catalysis to biological systems.

Some key features include:

• Formation: Occurs when a complex ion interacts with counterions to form a stable compound.
• Properties: They often exhibit unique spectroscopic, magnetic, and chemical behaviors.
• Applications: Widely used in medicinal chemistry as metal-based drugs or imaging agents.

The \([\text{Ni(en)(NH}_3\text{)}_3\text{(H}_2\text{O)]}^{2+}\) ion from our problem exemplifies how a complex is formed from nickel and ligands, demonstrating typical coordination compound characteristics.

Charge of Complexes

The charge of a coordination complex is the net result of the charges from its metal ion and attached ligands. Understanding this concept is crucial in determining the complex's chemical identity and its interactions.

When assessing the charge of a complex:

• Identify Charges: Determine the charge of the central metal and each ligand. Often, this requires recognizing common charges for metals and knowledge of ligand neutrality or charge.
• Calculate Net Charge: Combine charges. For \([\text{Ni(en)(NH}_3\text{)}_3\text{(H}_2\text{O)]}^{2+}\), only \(\text{Ni}^{2+}\) contributes, leading to an overall charge of \(+2\).
• Impact of Charge: It influences the complex’s solubility, interactions, and electrochemical properties.

Properly understanding the charge helps predict how the complex will behave in different environments, proving essential in coordination chemistry.