Problem 172 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following pairs represents linkage isomers? (a) \(\left[\mathrm{Pd}\left(\mathrm{P} \mathrm{Ph}_{3}\right)_{2}(\mathrm{NCS})_{2}\right]\) and \(\left[\mathrm{Pd}\left(\mathrm{P} \mathrm{Ph}_{3}\right)_{2}(\mathrm{SCN})_{2}\right]\) (b) \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{NO}_{3}\right] \mathrm{SO}_{4}\) and \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{5} \mathrm{SO}_{4}\right] \mathrm{NO}_{3}\) (c) \(\left[\mathrm{Pt} \mathrm{Cl}_{2}\left(\mathrm{NH}_{3}\right)_{4}\right] \mathrm{Br}_{2}\) and (d) \(\left[\mathrm{Cu}\left(\mathrm{NH}_{3}\right)_{4}\right]\left[\mathrm{Pt} \mathrm{Cl}_{4}\right]\) and \(\left[\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{4}\right]\left[\mathrm{CuCl}_{4}\right]\)

Step-by-Step Solution

Answer

Option (a) represents linkage isomers.

Step 1: Understanding Linkage Isomers

Linkage isomers occur when a ligand can bind to the central metal atom through different atoms. Common ligands with this property include NO2⁻ (nitro/nitrito) and SCN⁻ (thiocyanate/isothiocyanate).

Step 2: Analyzing Option (a)

In option (a), we have the complexes [Pd(PPh3)2(NCS)2] and [Pd(PPh3)2(SCN)2]. Here, the ligand NCS⁻/SCN⁻ is known for linkage isomerism. It can bind through nitrogen (NCS⁻) or sulfur (SCN⁻). Thus, option (a) represents linkage isomers.

Step 3: Analyzing Option (b)

In option (b), the complexes are [Co(NH3)5NO3]SO4 and [Co(NH3)5SO4]NO3. Here, the groups are swapping their positions between the coordination sphere and as a counterion, but there's no change in how the ligands are attached to the metal, so these are ionization isomers, not linkage isomers.

Step 4: Analyzing Option (c)

In option (c), the complex [PtCl2(NH3)4]Br2 does not involve any ligands capable of linkage isomerism, as all ligands and their binding modes are fixed. Therefore, this option does not contain linkage isomers.

Step 5: Analyzing Option (d)

In option (d), we have [Cu(NH3)4][PtCl4] and [Pt(NH3)4][CuCl4]. This involves a swap of the cation and anion complexes, but not a change in how individual ligands are attached to the metals. Thus, these compounds do not represent linkage isomers.

Key Concepts

Coordination Chemistry

Coordination chemistry focuses on the study of complex compounds formed when ions or molecules, known as ligands, bond to a central metal atom. These compounds are pivotal in various biochemical processes and industrial applications. At the heart of coordination chemistry is the coordination complex, which comprises a central transition metal atom or ion bonded to surrounding ligands.

The way in which these ligands bind to the central metal can significantly alter the chemical behavior and properties of the complex. For example, linkage isomers arise when a ligand alters the atom through which it is coordinated to the metal, without changing its overall composition. Understanding these concepts can provide insights into the roles these compounds play in catalysis, materials science, and biological systems.

• The central metal and ligands offer the unique geometrical structures of coordination complexes.
• Linkage isomerism is a fascinating phenomenon explored within the realm of coordination chemistry.

Complex Compounds

Complex compounds, or coordination compounds, consist of a central atom, usually a transition metal, surrounded by molecules or anions, called ligands. These compounds are often highlighted for their vibrant colors, conductivity, and magnetic properties, which arise from their unique electronic structures.

The coordination number of a central metal atom is determined by the number of ligand donor atoms attached to it. The geometry of these complexes can be octahedral, square planar, tetrahedral, and more, determined by the spatial arrangement required by ligands to minimize electron pair repulsion.

In the case of linkage isomers, like those found in the exercise (option a), the compound exhibits different properties depending on which atom (e.g., nitrogen or sulfur in SCN⁻) the ligand uses to bind to the metal.

Ligands

Ligands are ions or molecules that donate electrons to the central metal atom of a coordination complex. This donation forms coordinate covalent bonds, effectively stabilizing the complex and influencing its chemical properties and reactivity.

Ligands are classified based on their electron-pair-donating atoms, which can be classified as monodentate, bidentate, or polydentate, depending on the number of bonding sites per ligand molecule. Furthermore, ligands exhibit a variety of binding modes, such as linkage isomerism, where nitrogen and sulfur in the thiocyanate ligand (SCN⁻) bio can coordinate differently to the metal centre.

• Common ligands include water (H₂O), ammonia (NH₃), and chloride ions (Cl⁻).
• The way ligands bind affects the geometry and stability of coordination complexes.

Transition Metals

Transition metals are central to the formation of coordination complexes due to their ability to engage in various oxidation states and their possession of empty d orbitals. They are unique in forming stabilized complexes with multiple ligands, showcasing rich chemistries visible across the periodic table.

These metals are often involved in colorful complex formation seen in transition metal-based compounds. Their d electron configurations allow them to participate in complex electronic interactions that yield properties such as magnetism and electronic conductivity. In the context of linkage isomerism, the transition metal's affinity for electron-rich ligands enables distinct bond formations based on electronic preferences of the atoms involved in coordination.