Problem 26 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

As per IUPAC nomenclature, the name of the complex \(\left[\mathrm{Co}\left(\mathrm{H}_{2} \mathrm{O}\right)_{4}\left(\mathrm{NH}_{3}\right)_{2}\right] \mathrm{Cl}_{3}\) is : (a) Tetraaquadiaminecobalt (III) chloride (b) Tetraaquadiamminecobalt (III) chloride (c) Diaminetetraaquacoblat (II) chloride (d) Diamminetetraaquacobalt (III) chloride

Step-by-Step Solution

Answer

(d) Diamminetetraaquacobalt (III) chloride.

Step 1: Identify the Ligands

In the complex \( [\mathrm{Co}\left(\mathrm{H}_{2}\mathrm{O}\right)_{4}\left(\mathrm{NH}_{3}\right)_{2}] \mathrm{Cl}_{3} \), we have two types of ligands: water \((\mathrm{H}_2\mathrm{O})\) and ammonia \((\mathrm{NH}_3)\). The water ligand is called 'aqua' and the ammonia ligand is called 'ammine' in IUPAC nomenclature.

Step 2: Count the Number of Each Type of Ligand

The complex has four water ligands and two ammonia ligands. Therefore, it will be named as 'tetraqua' for the four water molecules, and 'diammine' for the two ammonia molecules.

Step 3: Identify the Metal and Its Oxidation State

The metal in the complex is cobalt (Co). The charge of the complex ion is balanced by three chloride ions \((\mathrm{Cl}^-)\), indicating that the oxidation state of cobalt must be +3. Thus, we use '(III)' to denote the oxidation state of the cobalt in the name.

Step 4: Compile the Name

According to IUPAC rules, the ligands are named in alphabetical order regardless of their number: 'diammine' comes before 'tetraqua'. Thus, the complete name is 'Diamminetetraaquacobalt(III) chloride', reflecting the ligands, the metal, and the charge of the complex ion.

Key Concepts

Coordination Chemistry

In coordination chemistry, we're concerned with the study of complex compounds that consist of a central metal atom or ion and surrounding molecules or ions known as ligands. These ligands form coordinate bonds with the metal center, creating coordination complexes. These compounds often have distinct properties and are important in various chemical processes. Coordination chemistry explores the interactions, structures, and roles of these complexes. Understanding how ligands interact with a central metal atom helps in predicting the stability and reactivity of complexes, which is crucial in both industrial applications and biological systems where metal complexes play key roles. Knowing this helps students to gain a foundation for understanding more complex topics in chemistry.

Oxidation States

Oxidation states are a reflection of the distribution of electrons between atoms in a molecule. For transition metals like cobalt in our exercise, identifying the correct oxidation state is crucial because it influences the chemical behavior and the nomenclature of the compound. In a coordination compound like \([\text{Co}\left(\text{H}_{2}\text{O}\right)_{4}\left(\text{NH}_{3}\right)_{2}] \text{Cl}_{3}\), cobalt is in the +3 oxidation state. This is deduced from the need to balance the charge of the entire compound, given that each chloride ion \((\text{Cl}^-)\) carries a -1 charge, and the neutral water and ammonia ligands do not affect the overall charge. Therefore, identifying the oxidation state aids in assigning the correct IUPAC name with the appropriate Roman numeral indication.

Ligand Naming

Ligand naming follows specific IUPAC rules and plays a key role in the nomenclature of coordination compounds. Ligands are the ions or molecules that donate a pair of electrons to the metal atom. Each type of ligand has a specific name based on its structure and charge. In the given complex, the ligands are water \((\text{H}_2\text{O})\) and ammonia \((\text{NH}_3)\). According to IUPAC conventions:

• Water is referred to as "aqua."
• Ammonia is referred to as "ammine."

Naming also involves prefixes to indicate the number of each ligand:

• 'Tetra' is used for four water molecules ("tetraqua").
• 'Di' is used for two ammonia molecules ("diammine").

Ligands are listed in alphabetical order in the complex's name, indigently of their quantity. This systematic approach ensures clarity and precision in chemical communication.

Complex Compounds

Complex compounds, also known as coordination compounds, are a pivotal part of modern chemistry. These compounds have a central metal atom or ion surrounded by various ligands that contribute to the compound's unique chemical and physical properties. In our example \([\text{Co}\left(\text{H}_{2}\text{O}\right)_{4}\left(\text{NH}_{3}\right)_{2}] \text{Cl}_{3}\), cobalt acts as the central metal ion, and is surrounded by aqua and ammine ligands. These compounds have significant implications in chemical reactions and applications such as catalysis, medicinal therapies, and in the development of new materials. Understanding complex compounds also aids in comprehending biological systems, where such complexes play critical roles in processes like oxygen transport and electron transfer. Mastery of complex compound nomenclature according to IUPAC rules not only helps in academic endeavors but also equips students with a vital tool for understanding the behavior and application of these compounds in various scenarios.