Question

Name the following ions or compounds. (a) \(\left[\mathrm{Co}\left(\mathrm{H}_{2} \mathrm{O}\right)_{4} \mathrm{Cl}_{2}\right]^{+}\) (c) \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right) \mathrm{Br}_{3}\right]^{-}\) (b) \(\operatorname{Co}\left(\mathrm{H}_{2} \mathrm{O}\right)_{3} \mathrm{F}_{3}\) (d) \(\left[\mathrm{Co}(\mathrm{en})\left(\mathrm{NH}_{3}\right)_{3} \mathrm{Cl}\right]^{2+}\)

Short answer

(a) tetra-aqua di-chloro cobalt(III) ion; (b) tri-aqua tri-fluoro cobalt(III); (c) ammine tri-bromo platinate(II); (d) ammine tri-chloro cobaltic(III) ion.

Step-by-step solution

Identify the Central Atom and Ligands (Part a)

For (a) \( \left[\mathrm{Co}\left(\mathrm{H}_{2} \mathrm{O}\right)_{4} \mathrm{Cl}_{2}\right]^{+} \),- The central atom is Cobalt (Co).- The ligands are water (\( \mathrm{H}_{2} \mathrm{O} \)), a neutral ligand, and chloride (\( \mathrm{Cl}^{-} \)), a negatively charged ligand.- The compound is cationic due to the positive charge.

Name the Ligands and Provide Prefixes (Part a)

- Water is named 'aqua' in coordination compounds. - Chloride is named with the suffix '-chloro.' - Use prefixes to indicate the number of each ligand: 'tetra' for four aqua and 'di' for two chloro.

Consider the Charge and Write the Name (Part a)

The charge on the complex is +1, and the oxidation state of cobalt is needed:Co is in the oxidation state +3 because \([\text{Co} + (4 \times 0) + (2 \times -1)] = +1\). Therefore, the name is:\[[\text{tetra-aqua di-chloro cobalt(III) ion}]\].

Identify the Central Atom and Ligands (Part b)

For (b) \( \operatorname{Co}\left(\mathrm{H}_{2} \mathrm{O}\right)_{3} \mathrm{F}_{3} \),- The central atom is Cobalt (Co).- The ligands are water \( \mathrm{H}_{2} \mathrm{O} \) and fluoride \( \mathrm{F}^{-} \).- This is a neutral compound (not an ion).

Name the Ligands and Provide Prefixes (Part b)

- 'Aqua' for water and 'fluoro' for fluoride. - The prefix 'tri' is used as both ligands happen in threes: 'tri-aqua tri-fluoro.'

Write the Name (Part b)

This complex has no overall charge, and cobalt is in the +3 oxidation state:\[[\text{tri-aqua tri-fluoro cobalt(III)}]\].

Identify the Central Atom and Ligands (Part c)

For (c) \( \left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right) \mathrm{Br}_{3}\right]^{-} \),- The central atom is Platinum (Pt).- The ligands are ammonia (\( \mathrm{NH}_{3} \)) called 'ammine' and bromide (\( \mathrm{Br}^{-} \)) called 'bromo'.- This compound is an anionic complex.

Name Ligands and Write the Name (Part c)

- Use the prefix 'tri' for the three bromides.- 'Ammine' for the single ammonia.- The oxidation state of platinum is +2:Since the overall charge is -1, \([\text{Pt} + 0 + (3 \times -1)] = -1\), therefore name is:\[\text{ammine tri-bromo platinate(II) ion}\].

Identify the Central Atom and Ligands (Part d)

For (d) \( \left[\mathrm{Co}( ext{en})\left(\mathrm{NH}_{3}\right)_{3} \mathrm{Cl}\right]^{2+} \),- The central atom is Cobalt (Co).- The ligands are ethylenediamine (en), ammonia (\( \mathrm{NH}_{3} \)) and chloride (\( \mathrm{Cl}^{-} \)).- Ethylenediamine is a bidentate ligand.

Calculate Oxidation and Write Name (Part d)

- Name ligands: 'en' for ethylenediamine, 'ammine' from ammonia, and 'chloro' for chloride.- The prefix 'tri' is used for three ammine.- The oxidation state of cobalt is +3 due to the formula \([\text{Co} + (2 \times 0) + (3 \times 0) + (-1)] = +2\):\[[\text{ammine tri-chloro cobaltic(III) ion}]\].

Key concepts

Naming Coordination Compounds

Naming coordination compounds involves a systematic approach based on the rules set by IUPAC (International Union of Pure and Applied Chemistry). This ensures clarity and uniformity across chemistry communities. When naming, always start with the naming of the ligands, followed by the central atom. If there are multiple ligands, name them alphabetically. Prefixes such as 'di-', 'tri-', 'tetra-' are used to denote the number of each type of ligand.
This gives an idea of what the compound would look like based on the formula. For example, in \(\left[\mathrm{Co}(\mathrm{H}_2\mathrm{O})_4\mathrm{Cl}_2\right]^+\), the ligands 'aqua' (for water) and 'chloro' (for chloride) are named first with their respective prefixes 'tetra-' and 'di-'. Cobalt is the central atom, and since the complex ion is cationic, we end the name with 'cobalt(III) ion'. This comes after determining the charge on the central atom, Cobalt(Co), which is indicated by Roman numerals in parentheses.
Learning the correct naming procedure increases understanding of compound composition and structure.

Ligands in Coordination Chemistry

Ligands play a crucial role in coordination chemistry. They are ions or molecules that bind to the central metal atom/ion in a coordination complex through coordinate bonds. These bonds are formed when the ligands donate a pair of electrons. Understanding the nature of ligands is essential, as they influence the properties and function of the coordination compounds.
The ligands can be neutral or charged. For example, in the complex \(\left[\mathrm{Pt}(\mathrm{NH}_3)\mathrm{Br}_3\right]^-\), ammonia (\(\mathrm{NH}_3\)) is a neutral ligand known as 'ammine', while bromide (\(\mathrm{Br}^-\)) is a negatively charged ligand called 'bromo'. The type of ligand affects the overall charge and stability of the coordination compound.
Furthermore, some ligands like ethylenediamine, used in the complex \(\left[\mathrm{Co}(\mathrm{en})(\mathrm{NH}_3)_3\mathrm{Cl}\right]^{2+}\), are described as bidentate because they can bond to the central atom at two sites. Understanding these types of ligands helps appreciate their binding strength and impact on the geometric configuration of complexes.

Oxidation States in Coordination Compounds

Determining the oxidation state of the metal in coordination compounds is vital for defining the compound's chemistry. This is because it affects the reactivity and interaction of the compound with other chemical entities. The oxidation state is calculated based on the charges of the ligands and the overall charge of the compound.
For instance, in \(\left[\mathrm{Pt}(\mathrm{NH}_3)\mathrm{Br}_3\right]^-\), the complex has an overall -1 charge. The three 'bromo' ligands contribute a -3 charge (since each \(\mathrm{Br}^-\) is -1), and the neutral 'ammine' ligand (ammonia) does not add or subtract any charge. Hence, the charge on Platinum is +2.

• Oxidation states are indicated in the name with Roman numerals, e.g., platinum(II) for a +2 oxidation state.
• Consistently accounting for all ligands' contributions and the overall charge ensures accurate determination of the metal's oxidation state.

Through understanding oxidation states, one gains valuable insight into the complex's potential chemical reactions and its stability.