Problem 185 - A Complete Resource Book in Chemistry for JEE Main

Question

A square planar complex is formed by hybridization of the following atomic orbitals \([2002]\) (a) \(s, p_{x}, p_{y}, p_{z}\) (b) s, \(\mathrm{p}_{\mathrm{x}}, \mathrm{p}_{y}, \mathrm{p}_{z}, \mathrm{~d}\) (c) \(\mathrm{d}_{\mathrm{x}}_{2}-\mathrm{y}^{2}, \mathrm{~s}, \mathrm{p}_{\mathrm{x}}, \mathrm{p}_{\mathrm{y}}\) (d) \(s, p_{x}, p_{y}, p_{z}, d_{z^{2}}\)

Step-by-Step Solution

Answer

Option (c) is correct: \\ d_{x^2-y^2}, s, p_{x}, p_{y} are used for square planar hybridization.

Step 1: Understanding Square Planar Complexes

Square planar complexes typically involve a central atom surrounded by other atoms or ligands in the same plane, forming a square. This type of geometry is often associated with coordination number 4 and is common for compounds of d8 metals, such as Pt(II) or Pd(II).

Step 2: Recognizing Hybridization in Square Planar Geometry

The square planar molecular geometry involves the dsp2 hybridization. This is typically achieved using one 's', two 'p', and one 'd' orbital. A key point is that the hybrid orbitals should include a d-orbital which allows for planar arrangement.

Step 3: Analyzing Each Option

We'll review each option to see which one matches the dsp2 hybridization needed for square planar geometry: (a) includes orbitals s, p(x), p(y), and p(z), allowing for sp3 hybridization but providing no d-orbital which is crucial for square planar. (b) includes one d-orbital but consists of 5 orbitals, suggesting sp3d which forms trigonal bipyramidal, not square planar. (c) includes d(x^2-y^2), s, p(x), and p(y) which perfectly fits the dsp2 hybridization. (d) includes a d(z^2) orbital, but sp3d is not suitable for square planar as mentioned in (b).

Key Concepts

Hybridization

Hybridization is a concept in chemistry where atomic orbitals mix to form new, equivalent hybrid orbitals. This mixing influences the geometry and bonding characteristics of molecules.
Hybrid orbitals are most often used in the description of covalent bonding. They provide a more accurate depiction of how atoms bond in molecules with non-linear geometries.

• Each type of hybridization corresponds to a certain geometric arrangement. For example, - sp hybridization results in a linear geometry. - sp2 hybridization gives rise to a trigonal planar geometry. - sp3 hybridization leads to a tetrahedral geometry.
• However, for square planar complexes, dsp2 hybridization comes into play. This involves mixing one d, one s, and two p orbitals.

Understanding hybridization helps explain the spatial arrangement and the type of bonds atoms form in a molecule.

dsp2

The dsp2 hybridization is atypical and arises when a central metal atom forms bonds in a square planar configuration. This is different from the more common sp3 hybridization.
In dsp2 hybridization, four orbitals mix together:

• One d orbital, specifically the d(x^2-y^2) orbital, which lies in the plane.
• One s orbital, mainly the 3s in the case of transition metals.
• Two p orbitals, usually p(x) and p(y), both oriented in the plane.

This hybridization is crucial for forming strong covalent bonds in square planar complexes. It is typically seen in complexes of transition metals like platinum (Pt) and palladium (Pd). Another reason for the preferred dsp2 configuration is the stability it provides due to the d(x^2-y^2) orbital's optimal overlap with ligand orbitals. Moreover, dsp2 hybridization is exceptional for accommodating electron-rich ligands, making it important in catalytic applications.

Coordination Number 4

The coordination number refers to the number of ligands attached to a central atom in a complex. It's a key factor in determining the geometry of the coordination complex.
For a coordination number of 4, typical molecular geometries include tetrahedral and square planar.

• Tetrahedral geometry often occurs in complexes without a d orbital, using sp3 hybridization.
• In contrast, square planar complexes, like those with dsp2 hybridization, are characteristic when strong field ligands cause a rearrangement of electronic configuration in metal ions, usually in d8 configurations.

Square planar configurations are less common than tetrahedral ones but are more prevalent in complex ions of heavier d-block metals. Examples include nickel(II), palladium(II), and platinum(II) complexes. Understanding the coordination number helps explain the bonding interactions and spatial arrangements of atoms in coordination chemistry.