Problem 21 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The number of geometric isomers that can exist for square planar complex \(\left[\mathrm{Pt}(\mathrm{Cl})(\mathrm{py})\left(\mathrm{NH}_{3}\right)\left(\mathrm{NH}_{2} \mathrm{OH}\right)\right]^{+}\)is \((\mathrm{py}=\) pyridine \()\) : (a) 4 (b) 6 (c) 2 (d) 3

Step-by-Step Solution

Answer

There are 3 geometric isomers.

Step 1: Identify the Coordination Geometry

The square planar complex has a coordination number of 4. This means the central metal, Pt, is bonded to four ligands which occupy vertices of a square plane.

Step 2: List the Ligands

The ligands in the complex are Cl, py (pyridine), NH3, and NH2OH. All these ligands are monodentate, meaning they each occupy one coordination site.

Step 3: Analyze the Positioning of Ligands

In a square planar complex, the positioning of ligands in adjacent (cis) or opposite (trans) positions determines the isomerism. You need to consider different ways these ligands can be arranged.

Step 4: Arrangement Possibilities

Consider varying two ligands at a time while keeping the remaining constant. Cl and py can occupy two adjacent positions (cis), while NH3 and NH2OH occupy the remaining two, leading to different arrangements and vice versa.

Step 5: Count the Different Isomers

By changing which ligand pairs are adjacent (cis) or opposite (trans), count all the distinct positional arrangements. This leads to the conclusion that there are 3 possible isomers.

Key Concepts

Square Planar Complexes

Square planar complexes are a fascinating aspect of coordination chemistry. This structure is most commonly found in complexes where a central metal atom is bonded to four ligands, each positioned at the corners of a square plane. This geometry arises because of specific electronic configurations and steric factors. When examining a typical square planar complex like \([\mathrm{Pt}(\mathrm{Cl})(\mathrm{py})\left(\mathrm{NH}_{3}\right)\left(\mathrm{NH}_{2} \mathrm{OH}\right)]^{+}\), you'll see the platinum (Pt) center is surrounded by these four ligands.

• This arrangement is distinct from other complex geometries, such as tetrahedral, which also involves four ligands but places them in a 3D formation.
• The square planar shape is especially seen in d⁸ metal ion complexes. Platinum(II) compounds, due to their electronic configuration, are excellent examples.
• The positioning allows for unique properties, such as being relatively stable and having distinct magnetic and spectroscopic characteristics.
  

In a square planar configuration, understanding the spatial arrangement is critical for predicting and explaining chemical behavior, especially in geometric isomerism.

Coordination Chemistry

Coordination chemistry focuses on the study of compounds formed between metal ions and ligands. A central theme here is how metals bond with other molecules or ions, known as ligands. These metal-ligand interactions shape the entire chemical and physical properties of the complexes.

• Ligands can be diverse, ranging from simple ions like Cl⁻ to larger organic molecules like pyridine.
• They coordinate to the metal center by donating electron pairs, thus forming coordinate covalent bonds.
• The arrangement and number of these ligands define the coordination number, which in the case of our complex is four.
  

In coordination chemistry, it's essential to grasp the link between ligand type and coordination geometry. This understanding allows for the prediction of reactivity, color, magnetism, and further chemical behavior of the complex.

Ligand Arrangement

In square planar complexes, the arrangement of ligands around the central metal is not just a matter of structure, but it directly impacts the properties and type of isomerism observed. With four ligands, there are multiple ways these can be positioned.

• Adjacent ligands are in a "cis" position. This arrangement can lead to different reactivity or changes in properties compared to other arrangements.
• When ligands are opposite each other, they are in a "trans" position. The choice of cis or trans affects the overall symmetry of the molecule.
• Geometric isomerism occurs when same-bonded atoms have different spatial orientations, leading to distinct forms or isomers.
  

For the complex \([\mathrm{Pt}(\mathrm{Cl})(\mathrm{py})\left(\mathrm{NH}_{3}\right)\left(\mathrm{NH}_{2}\mathrm{OH}\right)]^{+}\), determining the number of geometric isomers involves considering different cis-trans placements. In conclusion, three distinct geometric isomers can be formed by varying the configurations of cis and trans arrangements.