Question

What are the systematic names for the following ions and compounds? (a) \(\left[\mathrm{cis}-\mathrm{Co}(\mathrm{en})_{2} \mathrm{Cl}_{2}\right]^{+}\) (b) \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{Cl}\right] \mathrm{Cl}_{3}\) (c) \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{Cl}\right] \mathrm{Cl}_{2}\)

Short answer

(a) cis-bis(ethylenediamine)dichlorocobalt(III) ion; (b) pentaamminechloroplatinum(IV) chloride; (c) pentaamminechlorocobalt(III) chloride.

Step-by-step solution

Analyze the Complex Ion (a)

The complex ion in (a) is \( \left[\mathrm{cis}-\mathrm{Co}(\mathrm{en})_{2} \mathrm{Cl}_{2}\right]^{+} \). First, identify the components:- Central metal: Cobalt (Co)- Ligands: ethylenediamine (en) and chloride (Cl)The prefix `cis` indicates the 3D arrangement of ligands around the central metal, where the two chloride ions are on adjacent positions.

Name the Ligands in (a)

In the complex ion \( \left[\mathrm{cis}-\mathrm{Co}(\mathrm{en})_{2} \mathrm{Cl}_{2}\right]^{+} \):- Ethylenediamine (en) is a bidentate ligand, which means it forms two bonds with the central metal ion. The prefix 'bis' is used for bidentate ligands with multiple occurrences.- Chloride is a common monodentate ligand.

Determine Oxidation State for (a)

For \( \left[\mathrm{cis}-\mathrm{Co}(\mathrm{en})_{2} \mathrm{Cl}_{2}\right]^{+} \):- Ethylenediamine is a neutral ligand.- Each chloride ion has a charge of \(-1\).- The overall charge of the complex is \(+1\). Set up an equation: \( x + 0 \times 2 + (-1) \times 2 = +1 \).Solve for \( x \) to find the oxidation state of cobalt:\[ x = +3 \].

Assign the Systematic Name for (a)

The systematic name for \( \left[\mathrm{cis}-\mathrm{Co}(\mathrm{en})_{2} \mathrm{Cl}_{2}\right]^{+} \) is "cis-bis(ethylenediamine)dichlorocobalt(III) ion".

Analyze the Complex Compound (b)

The compound in (b) is \( \left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{Cl}\right]\mathrm{Cl}_{3} \). The components are:- The complex is \( \left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{Cl}\right]^{3+} \) because 3 chloride ions balance a \(-3\) charge outside the coordination sphere.- Central metal: Platinum (Pt)- Ligands: Ammonia (\( \mathrm{NH}_{3} \)), Chloride (Cl) as part of the coordination sphere.

Name the Ligands in (b)

In the complex ion \( \left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{Cl}\right]^{3+} \):- Ammonia (\( \mathrm{NH}_{3} \)) is neutral and called "ammine."- Chloride ion is named "chloro."

Determine Oxidation State for (b)

For \( \left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{Cl}\right]^{3+} \): - Ammonia is a neutral ligand.- Chloride has a \(-1\) charge.- Set up an equation: \( x + 0 \times 5 + (-1) = +3 \).Solve for \( x \) to get \( x = +4 \), which is the oxidation state of platinum.

Assign the Systematic Name for (b)

The systematic name for \( \left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{Cl}\right]\mathrm{Cl}_{3} \) is "pentaamminechloroplatinum(IV) chloride."

Analyze the Complex Compound (c)

For \( \left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{Cl}\right]\mathrm{Cl}_{2} \):- Inside the coordination sphere, the complex is \( \left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{Cl}\right]^{2+} \).- Central metal: Cobalt (Co)- Ligands: Ammonia (\( \mathrm{NH}_{3} \)), Chloride (Cl).

Name the Ligands in (c)

In \( \left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{Cl}\right]^{2+} \):- Ammonia is called "ammine" and contributes no charge.- Chloride ion in the complex sphere is named "chloro."

Determine Oxidation State for (c)

For \( \left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{Cl}\right]^{2+} \):- Ammonia ligands are neutral.- Chloride has a \(-1\) charge.- Equation: \( x + 0 \times 5 + (-1) = +2 \).Solve for \( x \) gives \( x = +3 \), the oxidation state of cobalt.

Assign the Systematic Name for (c)

The systematic name for \( \left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{Cl}\right]\mathrm{Cl}_{2} \) is "pentaamminechlorocobalt(III) chloride."

Key concepts

Coordination Chemistry

Coordination chemistry is a fascinating area in the field of chemistry that focuses on the study of coordination compounds, also known as complex compounds. These compounds consist of a central metal atom or ion, surrounded by molecules or anions known as ligands. Coordination compounds play a critical role in numerous biological systems and industrial processes.

• Coordination Sphere: This is where the metal ion and the directly attached ligands reside. The coordination sphere is usually enclosed in square brackets.
• Central Metal: In coordination compounds, the central metal atom or ion serves as the "anchor." It is most often a transition metal like cobalt (Co) or platinum (Pt).
• Complex Ion: When the coordination sphere carries a charge, it becomes a complex ion, which could be either positively or negatively charged depending on the balance of charges between the metal center and the ligands.

Understanding the nomenclature of these compounds involves identifying and naming each component based on systematic rules established by IUPAC. This helps in clearly communicating the structure and composition of complex compounds.

Ligands and Complex Ions

Ligands are crucial components of coordination chemistry. They are atoms, ions, or molecules that donate a pair of electrons to a metal atom or ion to form a coordination complex. The nature and number of ligands influence the physical and chemical properties of the complex.

Types of Ligands

• Monodentate Ligands: These attach to the metal atom at a single point. Common examples include chloride (Cl) and ammonia (NH₃).
• Bidentate Ligands: These form two bonds with the central metal ion. An example is ethylenediamine (en), often mentioned in contexts like cis-bis(ethylenediamine)dichlorocobalt(III) ion.

Complex Ions

When ligands bind with a central metal ion, they form a complex ion. The charge on the complex ion depends on the sum of the charges of the metal and the ligands. For example, both the complex ions \( [\text{Co} (\text{NH}_3)_5\text{Cl}]^{2+} \) and \( [\text{Pt} (\text{NH}_3)_5 \text{Cl}]^{3+} \) are formed by different combinations of neutral and charged ligands.

Oxidation States

The concept of oxidation states is essential for understanding the properties and naming of coordination complexes. An oxidation state is a number that represents the total number of electrons an atom gains, loses, or shares when it forms a chemical bond. In coordination compounds, it is crucial for balancing charges and determining the chemical formula.

Determining Oxidation States

• Identify all ligands and their charges, if any.
• Identify the overall charge of the complex ion, if given.
• Set up an equation that sums the charges of the metal and ligands to equal the charge of the complex. Solve for the oxidation state of the metal.

For instance, in the complex ion \( [\text{Co} (\text{en})_2 \text{Cl}_2]^{+} \), the ethylenediamine ligands are neutral, each chloride contributes a \(-1\) charge, and the whole complex ion has a \(+1\) charge. Solving the equation yields an oxidation state of +3 for cobalt. Understanding oxidation states is key to correct systematic nomenclature of coordination compounds.