Problem 29 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The IUPAC name of \(\left[\mathrm{Ni}\left(\mathrm{NH}_{3}\right)_{4}\right]\left[\mathrm{NiCl}_{4}\right]\) is (a) Tetrachloronickel (II) - tetraamminenickel (II) (b) Tetraamminenickel (II) - tetrachloronickel (II) (c) Tetraamminenickel (II) - tetrachloronickelate (II) (d) Tetrachloronickel (II) - tetrachloronickelate (0) Ans. (C)

Step-by-Step Solution

Answer

(c) Tetraamminenickel (II) - tetrachloronickelate (II)

Step 1: Identify the Cation and Anion

The given complex is \([\text{Ni(NH}_3)_4][\text{NiCl}_4]\). Here, \([\text{Ni(NH}_3)_4]^2+\) is the cation and \([\text{NiCl}_4]^{2-}\) is the anion.

Step 2: Naming the Cation

The cation \([\text{Ni(NH}_3)_4]^2+\) consists of Ni(II) surrounded by four ammonia \(\text{(NH}_3\) ligands. Ammonia in coordination compounds is called ammine. Therefore, it is named as tetraamminenickel (II) indicating four amine ligands.

Step 3: Naming the Anion

The anion \([\text{NiCl}_4]^{2-}\) consists of Ni(II) surrounded by four chloride (Cl) ligands. For anionic complexes, the metal name ends with 'ate', and thus, this is called tetrachloronickelate (II). Also, it reflects the oxidation state of nickel in brackets.

Step 4: Combine Cation and Anion Names

The complete name of the complex is formed by writing the cation name first followed by the anion name. Thus, the IUPAC name is Tetraamminenickel (II) - tetrachloronickelate (II).

Key Concepts

Coordination Compounds

Coordination compounds are interesting and important in chemistry because they involve complex structures composed of central metal atoms or ions bonded to surrounding molecules or ions, known as ligands. These ligands are capable of donating one or more pairs of electrons to the metal. This forms a coordinate covalent bond, creating a complex ion.

The metal ion in the complex acts as a Lewis acid, while the ligands act as Lewis bases. The arrangement and type of ligands can significantly affect the properties and stability of the coordination compound.

• Central metal ion/atom: This is typically a transition metal that has vacant orbitals to accept electron pairs from ligands.
• Ligands: These are ions or molecules attached to the central metal, each donates a pair of electrons to the metal.
• Coordinate number: The number of ligand donor atoms bonded to the central atom, usually ranging from two to nine.

Understanding coordination compounds is fundamental in chemistry as they appear in various chemical reactions, including biological systems and industrial processes. An example is \([\text{Ni(NH}_3)_4][\text{NiCl}_4]\), where nickel acts as the central metal atom.

Cation and Anion Identification

To properly name a coordination compound, it's crucial to identify the complex's cations and anions. These components can determine the sequence in which parts of the compound's name are compiled. When looking at the given complex \([\text{Ni(NH}_3)_4][\text{NiCl}_4]\), we find distinct cationic and anionic species.

Cation identification is based on the neutral ligand count and the presence of charges, while anion identification often relates to the type and charge of ligands.

• Cation \([\text{Ni(NH}_3)_4]^{2+}\): This consists of nickel surrounded by ammine ligands. Here, ammonia molecules donate electron pairs, resulting in a positive charged complex.
• Anion \([\text{NiCl}_4]^{2-}\): This complex comprises nickel and chloride ions, which, when together, form an overall negative charge.

When naming, always start with the name of the cation followed by the anion. Proper identification is key to constructing the IUPAC name correctly.

Oxidation States

Oxidation states in coordination compounds reveal the apparent charge on the central metal atom when bonded with its ligands. Determining the oxidation state is essential for correctly naming and understanding the chemical behavior of such compounds. In the example ⚬\( [\text{Ni(NH}_3)_4]^{2+} \) and \( [\text{NiCl}_4]^{2-} \), identifying the oxidation states helps in naming the compound.

Each ligand type has its own neutral or charge attributes, affecting the metal's oxidation state.

• The metal usually takes a positive oxidation state since ligands can neutralize positive charges with their electron donation. Nickel, in our complex, holds a \(+2\) oxidation state, as revealed by the charge balance with ligands.
• Aqueous or neutral ligands (like \(\text{NH}_3\)): These typically do not possess a charge themselves and contribute to the overall neutrality of the complex.
• Electronegative or anionic ligands (like \(\text{Cl}^-\)): These lend negative charges which are balanced by the positive oxidation state of the metal.

Clearly stating the oxidation state in the compound name helps chemists and students to understand its electronic structure and reactivity better. For example, in \(\text{Tetraamminenickel (II) - tetrachloronickelate (II)}\), the Roman numeral \((\text{II})\) indicates nickel's oxidation state.