Problem 48 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Write down the IUPAC names of the following compounds: (i) \(\left[\mathrm{Cr}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{CO}_{3}\right] \mathrm{Cl}\) (ii) \(\mathrm{K}_{3}\left[\mathrm{Cr}(\mathrm{CN})_{6}\right]\) (iii) \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{ONO}\right] \mathrm{Cl}_{2}\)

Step-by-Step Solution

Answer

(i) Pentaamminecarbonatochromium(III) chloride (ii) Potassium hexacyanochromate(III) (iii) Pentaamminenitritocobalt(III) chloride

Step 1: Identify the Central Metal and Ligands

First, identify the central metal and the ligands associated with it in each compound.(i) In \([\mathrm{Cr}(\mathrm{NH}_{3})_{5} \mathrm{CO}_{3}] \mathrm{Cl}\), the central metal is chromium (Cr) with ligands ammonia (NH₃) and carbonate (CO₃). (ii) In \(\mathrm{K}_{3}[\mathrm{Cr}(\mathrm{CN})_{6}]\), the central metal is chromium (Cr) with ligands cyanide (CN). (iii) In \([\mathrm{Co}(\mathrm{NH}_{3})_{5} \mathrm{ONO}] \mathrm{Cl}_{2}\), the central metal is cobalt (Co) with ligands ammonia (NH₃) and nitrito (ONO).

Step 2: Determine the Charge on Complex Ion

Calculate the oxidation state of the central metal by using the charges of the ligands and counter ions. (i) Ammonia is neutral, carbonate is -2, chloride counter ion is -1, so chromium is +3. (ii) Cyanide is -1, potassium is +1, hence chromium is +3. (iii) Ammonia is neutral, nitrito is -1, chloride counter ions contribute -2, cobalt is +3.

Step 3: Assemble the Name Using Ligands and Metal

Write the name of the coordination compound by listing the ligands alphabetically followed by the central metal and its oxidation state in roman numerals. (i) The ligands are ammine and carbonato: 'pentaamminecarbonatochromium(III) chloride'. (ii) The ligand is cyano: 'potassium hexacyanochromate(III)'. (iii) The ligands are ammine and nitrito: 'pentaamminenitritocobalt(III) chloride'.

Step 4: Check for Naming Naming Rules

Ensure that the naming conventions such as prefixes for number of ligands, the suffix -ate if the complex is anion, are correctly followed. (i) No changes needed as nonspecific counter ions are outside the bracket. (ii) Apply -ate suffix: 'chromate'. (iii) Naming follows the convention as Co complex is charged.

Key Concepts

Central Metal Ion

In coordination chemistry, the central metal ion plays a crucial role in forming coordination compounds. It serves as the core around which the compound is structured.
Central metal ions are typically transition metals, which have vacant d orbitals allowing them to form complexes by bonding with ligands.

• The type of metal ion used can significantly impact the properties of the compound, including its color, magnetic properties, and reactivity.
• Examples from the compounds given are chromium (Cr) and cobalt (Co)—both are transition metals and commonly appear as central ions in coordination compounds.

Understanding the central metal ion is essential because it also influences the compound's overall geometry and stability.

Oxidation State

Determining the oxidation state of the central metal ion is a fundamental step in naming coordination compounds using IUPAC nomenclature. This is crucial because it directly affects the properties and reactivity of the coordination compound.
The oxidation state is found by balancing the charges contributed by ligands and any counter ions present.

• Neutral ligands, like ammonia, contribute zero charge.
• Anionic ligands, like carbonate and nitrito, contribute negative charges.
• Cations, such as potassium ions ( ext{K}^+ ), contribute positive charges in balancing the complex charge.

For the complexes given, chromium and cobalt both present an oxidation state of +3, which contributes to stabilizing the complex and affects its chemical behavior.

Ligand Naming

Ligand naming is a key component of the IUPAC nomenclature rules for coordination compounds. Ligands are the molecules or ions that donate pairs of electrons to the central metal ion to form the coordination compound. Proper naming follows specific conventions to ensure clarity and consistency.

• Ligands are listed in alphabetical order when writing the name of the compound, irrespective of their charge or nature.
• Neutral ligands, such as ammonia, are given specific names (like 'ammine').
• Anionic ligands often have names ending with ‘-o,’ such as 'carbonato' for carbonate ( ext{CO}_3^ {2-} ).
• Prefixes like mono-, di-, tri-, etc., indicate the number of each type of ligand.

In the examples provided, ammonia and cyanide ligands are named 'ammine' and 'cyano', respectively, reflecting these conventions clearly.

Coordination Chemistry

Coordination chemistry is the study of compounds formed between metal ions and ligands. Understanding this enables us to predict the properties and behavior of such substances.
Coordination compounds have diverse applications, from industrial catalysts to biological systems. Key points include:

• Coordination compounds can show a wide range of geometries, often dictated by the central metal ion and the number and type of ligands attached.
• These geometries include linear, tetrahedral, square planar, and octahedral, each determined by ligand arrangement around the central metal.
• Coordination chemistry also involves understanding the stability of these complexes, often influenced by the oxidation state, ligand charge, and the metal's nature.

In our cases, the compounds around chromium and cobalt exhibit coordination chemistry principles by forming stable complexes typical of transition metal ions.