Question

The ionization isomer of \(\left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{4} \mathrm{Cl}\left(\mathrm{NO}_{2}\right)\right] \mathrm{Cl}\) is A) \(\left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{4}\left(\mathrm{O}_{2} \mathrm{~N}\right)\right] \mathrm{Cl}_{2}\) B) \(\left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{4} \mathrm{C} 1_{2}\right]\left(\mathrm{NO}_{2}\right)\) C) \(\left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{4} \mathrm{Cl}(\mathrm{ONO})\right] \mathrm{Cl}\) D) \(\left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{4} \mathrm{Cl}_{2}\left(\mathrm{NO}_{2}\right)\right] \cdot \mathrm{H}_{2} \mathrm{O}\)

Short answer

D) \( \left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{4} \mathrm{Cl}_{2}\left(\mathrm{NO}_{2}\right)\right] \cdot \mathrm{H}_{2} \mathrm{O} \)

Step-by-step solution

Understanding Ionization Isomers

Ionization isomers are compounds that have the same composition but differ by which atoms or groups are found as part of the coordination sphere of the metal and which as counterions outside of the coordination sphere. In ionization isomers, the exchange occurs between ligands inside the coordination sphere and ions outside of it that are not coordinated to the central metal atom.

Identify the Original Coordination Compound

Identify the provided compound \( \left[\mathrm{Cr}\left(\mathrm{H}_{2}\mathrm{O}\right)_{4} \mathrm{Cl}\left(\mathrm{NO}_{2}\right)\right]\mathrm{Cl} \) and notice that chlorine (Cl) and nitrito group (NO2) are present inside the coordination sphere while another chlorine is acting as a counterion.

Predict the Ionization Isomer

To find the ionization isomer, one of the ligands in the coordination sphere is exchanged with the counterion. The nitrito group (NO2) or the chlorine (Cl) can switch places with the chlorine counterion outside of the coordination sphere.

Inspect the Options

Review each provided option and determine which one represents a true ionization isomer by checking if only the positions of the anions have been swapped without changing the overall formula.

Choose the Correct Option

Option D) \( \left[\mathrm{Cr}\left(\mathrm{H}_{2} \mathrm{O}\right)_{4} \mathrm{Cl}_{2}\left(\mathrm{NO}_{2}\right)\right] \cdot \mathrm{H}_{2} \mathrm{O} \) correctly shows the chlorine inside the coordination sphere and the nitrito group as a separate anion, hence it represents a valid ionization isomer of the given compound.

Key concepts

Coordination Compounds

Coordination compounds are fascinating chemical entities central to a myriad of chemical processes, including those in biological systems and industrial applications. They consist of a central metal atom or ion surrounded by molecules or ions called ligands. The central metal and its surrounding ligands form what is known as the coordination sphere, which is usually enclosed in square brackets when written in chemical formulas.

For example, in the coordination compound \(\left[\mathrm{Cr}\left(\mathrm{H}_{2}\mathrm{O}\right)_{4} \mathrm{Cl}\left(\mathrm{NO}_{2}\right)\right]\mathrm{Cl}\), chromium (Cr) is the central metal ion, and it is coordinated by four water molecules and one chloride ion as ligands, with a nitrito group also inside the coordination sphere. Another chloride ion is present outside this sphere, serving as a counterion balancing the charge of the complex.

Coordination compounds are characterized by specific numbers called coordination numbers, which represent the total number of ligand attachment points to the central atom. The coordination number of a metal ion in a coordination compound is determined by the number of these points, not necessarily the number of ligands, as some ligands can attach at multiple points.

Ligands in Coordination Chemistry

Ligands are ions or molecules that bind to a central metal atom to form coordination compounds. They play a crucial role in determining the reactivity, structure, and color of these compounds. Ligands can be charged or neutral and are often referred to as complexing agents because they can form complex ions with metals.

The nature of the ligands, their charge, size, and the type of atoms involved in bonding can significantly influence the properties of the coordination compound. In the world of coordination chemistry, ligands can be classified based on their denticity, or the number of donor atoms they possess. For example, water molecules in the compound above are monodentate ligands, binding through a single donor atom, while others like ethylenediamine (en) are bidentate, offering two atoms for coordination.

Furthermore, when ligands are substituted in a coordination compound, as seen in the concept of ionization isomers, their spatial arrangement and electronic properties can create vastly different compounds, despite having the same chemical formula. This substitution leads to unique chemical and physical properties, which are vital topics explored under JEE Advanced Chemistry.

JEE Advanced Chemistry

JEE Advanced Chemistry is a significant portion of one of the most competitive entrance exams for engineering colleges in India, including the prestigious IITs. The syllabus covers a broad range of topics including physical, organic, and inorganic chemistry.

Within the realm of inorganic chemistry, coordination compounds and their isomers are key concepts that students must master. Understanding the formation and properties of these compounds, as well as the different types of isomerism they exhibit, is crucial. Ionization isomerism, such as exemplified in the exercise solution involving the compound \(\left[\mathrm{Cr}\left(\mathrm{H}_{2}\mathrm{O}\right)_{4} \mathrm{Cl}\left(\mathrm{NO}_{2}\right)\right]\mathrm{Cl}\), is just one form of isomerism that can be tested in the JEE Advanced Chemistry paper.

Students are expected to have a firm grasp of concepts like ligand exchange, where predicting the outcome of such reactions requires a clear understanding of how ligands and counterions interact within coordination compounds. Therefore, excellence in this topic not only improves their chances of scoring well in the examination but also builds a solid foundation for future studies in chemistry and related fields.