Which of the following pairs of isomers and types of isomerism are correctly matched? (1) \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5}\left(\mathrm{NO}_{2}\right)\right] \mathrm{Cl}_{2}\) and \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5}(\mathrm{ONO})\right] \mathrm{Cl}_{2}\) (2) \(\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right]\left[\mathrm{Pt} \mathrm{Cl}_{4}\right]\) and \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{4}\right]\left[\mathrm{CuCl}_{4}\right]\) (3) \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Cl}_{2}\right] \mathrm{Br}_{2}\) and \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Br}_{2}\right] \mathrm{Cl}_{2}\) Select the correct answer using the codes given below: (a) 1 and 2 (b) 2 and 3 (c) 1 and 3 (d) 1,2 and 3

Linkage isomerism occurs in coordination compounds when a ligand is capable of coordinating to the central metal atom through two or more different atoms. An example of a ligand that exhibits this behavior is the nitrito group, which can bind through the nitrogen atom (forming a nitro compound) or the oxygen atom (producing a nitrito compound).

In the provided exercise, linkage isomerism is exemplified in the first set of compounds: \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5}\left(\mathrm{NO}_{2}\right)\right] \mathrm{Cl}_{2}\) and \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5}(\mathrm{ONO})\right] \mathrm{Cl}_{2}\). These two complexes comprise the same central metal and ligands, but the nitrito group coordinates differently, illustrating a textbook case of linkage isomerism.

To further grasp this concept, one should consider the geometry and electronic structure of the ligand involved, as well as the properties of the metal to which it coordinates. By understanding these factors, one can predict potential linkage isomers and their unique chemical and physical properties.

Ion exchange isomerism, also known as coordination sphere exchange isomerism, is a form of isomerism where ligands inside the coordination sphere of a complex ion exchange places with ions outside the coordination sphere. In such isomers, the molecular formula remains the same, but the properties may differ significantly, including solubility, color, and reactivity due to the change in coordination environment.

The third set of compounds from the exercise, \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Cl}_{2}\right] \mathrm{Br}_{2}\) and \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{4} \mathrm{Br}_{2}\right] \mathrm{Cl}_{2}\), demonstrates ion exchange isomerism. The chloride and bromide ions switch positions between the inner coordination sphere and the outer sphere of the complex ions. This type of isomerism can be particularly important when considering the biological activity of coordination compounds, as the specific ligands bound to the metal center might be essential for the compound's function.

Coordination chemistry is the study of compounds that form between metallic elements and various organic or inorganic ligands. A ligand is a molecule or ion that can donate a pair of electrons to the metal, forming a coordinate covalent bond. The resulting complexes have distinctive structures, properties, and behaviors that are affected by the nature of the metal ion and the ligands.

Key concepts within coordination chemistry include oxidation state, coordination number, and coordination polyhedra, representing the number of ligand-metal interactions and the spatial arrangement of these ligands around the central atom, respectively. Coordination compounds are pervasive in nature and technology, with applications ranging from catalysis and materials science to medicine and environmental remediation.

By studying the subtleties of how ligands attach to and interact with metal ions, chemists can design new compounds with desired properties for various applications. The scenarios presented in the exercise are practical examples that help students understand the complex nature of these interactions and the resulting consequences for compound behavior.