Problem 41 - A Complete Resource Book in Chemistry for JEE Main

Question

The IUPAC name for \(\mathrm{K}_{2}\left[\mathrm{OsCl}_{5} \mathrm{~N}\right]\) is (a) potassium pentachloroazidoosmate(VIII) (b) potassium pentachloroazidoosmate(VI) (c) potassium pentachloronitridoosmate(VI) (d) potassium nitroosmate(III)

Step-by-Step Solution

Answer

The correct IUPAC name is: potassium pentachloronitridoosmate(VI).

Step 1: Identify the coordination entity

The formula \(\mathrm{K}_{2}\left[\mathrm{OsCl}_{5} \mathrm{~N}\right]\) contains the coordination complex \([\mathrm{OsCl}_{5} \mathrm{~N}]^{2-}\). The central metal atom is osmium (Os), and the ligands are five chloride ions (Cl) and one nitride ion (N).

Step 2: Determine the oxidation state of the metal

Assign oxidation states to the ligands: chlorine (Cl) is -1 each, and nitride (\(\mathrm{N^{3-}}\)) is -3. The total charge contributed by ligands is \(-1 \times 5 - 3 = -8\). Since the complex has a 2- charge, set up the equation: \(\mathrm{Os} + (-8) = -2\), which simplifies to \(\mathrm{Os} = +6\). Thus, osmium is in the +6 oxidation state.

Step 3: Name the ligands

The anion ligands are named as follows: chloride becomes 'chloro' and nitride becomes 'nitrido' as a ligand.

Step 4: Name the coordination sphere

Combine the ligand names and the central metal with its oxidation state in Roman numerals: pentachloronitridoosmate(VI). The '-ate' suffix indicates that the complex is an anion.

Step 5: Name the cation

The cation \(\mathrm{K}_{2}\) is named 'potassium', and it appears before the anionic coordination complex.

Step 6: Complete the compound name

Combine the cation and the anionic coordination complex: 'potassium pentachloronitridoosmate(VI)'. This gives us the full IUPAC name.

Key Concepts

Oxidation State

Understanding the oxidation state of a metal in a coordination compound is crucial. This is because it affects the properties and reactions of the compound. The oxidation state is the effective charge of the metal atom. It is determined by the formal assignment of electrons in the ligands bonded to it.

In the example of \([\text{OsCl}_5 \text{~N}]^{2-}\), the oxidation state of osmium is deduced by considering the charges on the ligands. Each chloride ion has an oxidation state of -1, and the nitride ion is -3. Adding these contributions gives a total ligand-induced charge of -8. Since the entire complex is \(2-\), we set up the equation \( ext{Os} + (-8) = -2\), solving for \( ext{Os}\) results in an oxidation state of +6.

Understanding this helps appreciate the behavior of the compound during reactions. It influences factors like stability, color, and magnetic properties.

IUPAC Naming

IUPAC naming for coordination compounds ensures that there is no ambiguity when identifying chemical compounds. This system provides a set of rules to assign a unique name to every compound, which describes its structure.

• Identify the Order: First, list the names of the ligands in alphabetical order.
• Name the Central Metal: After the ligands, specify the name of the central metal followed by its oxidation state in Roman numerals in parentheses.
• Use of Suffix: If the complex is anionic, add the suffix '-ate' to the metal's name.

For the compound \(\text{K}_{2}[\text{OsCl}_5 \text{~N}]\), the systematic IUPAC name is 'potassium pentachloronitridoosmate(VI)', indicating a potassium cation, chloro and nitrido ligands around the osmium metal in +6 oxidation state.

Ligands

Ligands are the atoms or molecules that are bonded to the central metal in a coordination compound. They donate at least one pair of electrons to form a coordinate bond with the metal, significantly impacting the compound's structure and properties.

Ligands are named differently once they become part of a coordination complex. Anionic ligands typically end in 'o'. For example, chloride becomes 'chloro' and nitride becomes 'nitrido'.

• Chloro: Originates from chloride ions \(\text{Cl}^-\).
• Nitrido: Comes from nitride ions \(\text{N}^{3-}\).

The sequence and name of ligands help in accurately depicting the structure of the complex. Understanding ligands is important as they dictate many physical and chemical behaviors of coordination complexes.

Coordination Chemistry

Coordination chemistry is the study of compounds that feature coordinate bonds between a central metal atom and its surrounding ligands. It has profound implications in fields such as catalysis, material science, and biochemistry.

The coordination sphere refers to the combination of the central atom and the attached ligands. For example, in the compound \(\text{K}_{2}[\text{OsCl}_5 \text{~N}]\), the coordination sphere is \(\text{[OsCl}_5 \text{~N}]^{2-}\).

• Forms complex structures leading to diverse chemical reactivity.
• Includes unique properties like variable oxidation states, which enable various reactions.
• Understanding this concept arranges the framework to predict the behaviour of compounds in reactions.

Coordination chemistry not only enhances our understanding of inorganic compounds but also lays down foundational concepts for advanced chemical synthesis and applications in various industries.