Writing Formulas of Coordination Compounds: Videos & Practice Problems

When writing formulas for coordination compounds, follow three key rules: first, the cation precedes the anion; second, in complex ions, the transition metal is listed before ligands; and third, neutral ligands are alphabetically ordered before anionic ligands. Understanding these rules is essential for accurately representing complex ions and their structures, which are crucial in various chemical reactions and applications, including acid-base reactions and coordination chemistry.

Writing Formulas

When writing chemical formulas for coordination complexes, it is essential to adhere to three primary rules to ensure accuracy and clarity. The first rule emphasizes that the cation must be written before the anion. In this context, the cation can be either a counter ion or a complex ion, while the anion can also be a complex ion or a simple anion.

The second rule pertains to the arrangement of transition metals and ligands within complex ions. Specifically, the transition metal should be listed before the ligands. This is crucial for maintaining the correct structure of the coordination compound.

Finally, the third rule states that neutral ligands should be written before anionic ligands, and both types of ligands should be arranged in alphabetical order. This systematic approach helps in accurately representing the composition of the coordination complex.

By following these three rules—cation before anion, transition metal before ligands, and neutral ligands before anionic ligands in alphabetical order—you can effectively write the formulas for various coordination complexes and compounds.

Writing Formulas of Coordination Compounds Example

To derive the formula for tri-aquadibromocarbonylmanganese(III) chloride, we begin by identifying the components of the coordination compound. The cation is manganese(III), represented as \( \text{Mn}^{3+} \), and the anion is chlorite, denoted as \( \text{ClO}_2^{-} \).

Next, we list the ligands and their quantities. The term "triaqua" indicates three water molecules, which are neutral ligands, represented as \( \text{H}_2\text{O} \). The "dibromo" indicates two bromine atoms, which are anionic ligands, represented as \( \text{Br}^{-} \). The "carbonyl" refers to a carbon monoxide molecule, represented as \( \text{CO} \).

Now, we organize the components in the correct order for the complex ion. The transition metal is written first, followed by the neutral ligands and then the anionic ligands, all in alphabetical order. Thus, we have:

\( \text{[H}_2\text{O}]_3\text{CO}\text{Br}_2\text{Mn}^{3+} \)

Next, we calculate the overall charge of the complex ion. The manganese contributes a charge of \( +3 \), while the two bromide ions contribute a total of \( -2 \) (since each bromide ion has a charge of \( -1 \)). Therefore, the overall charge of the complex ion is:

\( +3 - 2 = +1 \)

Now, we can write the complete formula for the coordination compound. The cation (the complex ion) is written first, followed by the anion. Since the charges balance out, we can combine them without additional subscripts. The final formula for tri-aquadibromocarbonylmanganese(III) chloride is:

\( \text{[H}_2\text{O}]_3\text{CO}\text{Br}_2\text{Mn}^{3+} \cdot \text{ClO}_2^{-} \)

Write a formula for following coordination compound: sodium tris(ethylenediamine)oxalatonickelate(I).

• A. Na₂[Ni(en)₃CO₂]
• B. Na[Ni(NH₃)₃CO₂]
• C. Na[Ni(en)₃C₂O₄]
• D. Na[Ni(NH₃)₃C₂O₄]

Answer: (C)

What would be the formula for dibromotetracarbonylstannate(IV) sulfate.

• A. [Sn(CO)₄(Br)₂](SO₄)₂
• B. [Sn(CO)₄(Br)₂]SO₄
• C. [Sn(C₂O₄)₄(Br)₂](SO₄)₂
• D. [Sn(C₂O₄)₄(Br)₂]SO₄

Answer: (B)

Here’s what students ask on this topic:

What are the main rules for writing formulas of coordination compounds?

When writing formulas for coordination compounds, follow these main rules: Rule 1: The cation is written before the anion. Cations and anions can be either counter ions or complex ions. In complex ions, the transition metal is written before the ligands. Neutral ligands are listed before anionic ligands, and both are organized alphabetically. These rules are essential for writing formulas for coordination complexes or compounds.

How do you determine the order of ligands in a coordination compound formula?

In a coordination compound formula, ligands are ordered based on their type and alphabetical order. Neutral ligands are written before anionic ligands. Within each category (neutral or anionic), ligands are listed alphabetically. For example, in the complex ion [Cr(NH₃)₃(Cl)₃], NH₃ (a neutral ligand) is listed before Cl^- (an anionic ligand), and both are in alphabetical order.

Why is the transition metal written before ligands in complex ions?

The transition metal is written before the ligands in complex ions to clearly indicate the central atom around which the ligands are coordinated. This convention helps in understanding the structure and composition of the complex ion. For example, in [Fe(CN)₆]^4-, Fe is the central transition metal, and CN^- are the ligands.

Can you provide an example of writing a coordination compound formula from its name?

Sure! Let's write the formula for the coordination compound named 'tetraamminecopper(II) sulfate'. First, identify the cation and anion: 'tetraamminecopper(II)' is the cation, and 'sulfate' is the anion. The cation is a complex ion with copper as the central metal and four ammonia (NH₃) ligands. The formula for the cation is [Cu(NH₃)₄]²⁺. The anion is sulfate (SO₄)^2-. Combining them, the formula is [Cu(NH₃)₄]SO₄.

What is the significance of alphabetical order in writing formulas of coordination compounds?

Alphabetical order is significant in writing formulas of coordination compounds to maintain consistency and clarity. It ensures that the ligands are listed in a standardized manner, making it easier to interpret and compare different compounds. For example, in the complex ion [Co(NH₃)₅Cl]²⁺, NH₃ (ammonia) is listed before Cl^- (chloride) because 'A' (ammonia) comes before 'C' (chloride) alphabetically.