Problem 168 - A Complete Resource Book in Chemistry for JEE Main

Question

Which one of the following has a square planar geometry? [2007] (a) \(\left[\mathrm{FeCl}_{4}\right]^{2}\) (b) \(\left[\mathrm{NiCl}_{4}\right]^{2}\) (c) \(\left[\mathrm{PtCl}_{4}\right]^{2-}\) (d) \(\left[\mathrm{CoCl}_{4}\right]^{2-}\)

Step-by-Step Solution

Answer

The complex with square planar geometry is \\( \left[\mathrm{PtCl}_{4}\right]^{2-} \\).

Step 1: Understanding Square Planar Geometry

Square planar geometry is typically observed in coordination complexes with a central transition metal atom bound to four ligands in a plane, forming a square. This geometry is common for d8 electron configuration metal ions, like Ni(II), Pd(II), and Pt(II).

Step 2: Analyzing Each Coordination Complex

We need to determine the oxidation state and electron configuration for the metal ions in each complex to identify the d8 systems. (a) \(\left[\mathrm{FeCl}_{4}\right]^{2-} \) - Iron commonly exists in oxidation states +2 and +3; \(\mathrm{Fe}^{2+} \) is d6. (b) \(\left[\mathrm{NiCl}_{4}\right]^{2-} \) - Nickel(II) has a d8 configuration, but tends to form tetrahedral rather than square planar complexes. (c) \(\left[\mathrm{PtCl}_{4}\right]^{2-} \) - Platinum(II) is a d8 system and commonly forms square planar complexes.(d) \(\left[\mathrm{CoCl}_{4}\right]^{2-} \) - Cobalt(II) is a d7 configuration which does not favor square planar geometry.

Step 3: Selecting the Complex with Square Planar Geometry

Given that d8 electron configuration metal ions like Pt(II) often exhibit square planar geometry, and analyzing the oxidation states and electron configurations, \(\left[\mathrm{PtCl}_{4}\right]^{2-} \) is the only complex that aligns with square planar geometry.

Key Concepts

Coordination Complexes

Coordination complexes are fascinating chemistry structures formed when a central metal atom or ion binds to a specific number of molecules or ions, known as ligands. These complexes are prevalent in the world of inorganic chemistry and play a crucial role in various biological, chemical, and industrial processes. Understanding coordination complexes aids in predicting the geometry of these compounds, which significantly impacts their physical and chemical properties.

In a coordination complex, the central metal is usually a transition metal, capable of forming multiple bonds. Ligands, which can be anions or neutral molecules, donate electron pairs to the metal center, creating a coordinate covalent bond. The number of ligands attached to the metal is termed the coordination number, and it helps determine the complex's geometry.

• Common geometries include tetrahedral, square planar, and octahedral.
• The type of ligands and the oxidation state of the metal influence the geometry.

Coordination complexes can display numerous geometries with each type influencing the properties, including reactivity and color, of the complex.

d8 Electron Configuration

The term 'd8 electron configuration' refers to a specific arrangement of electrons in the d orbital, often observed in transition metals. In this configuration, there are eight electrons distributed within five d orbitals. Understanding electronic configuration is essential as it plays a vital role in determining the chemical behavior and geometry of the complexes.

For a metal ion with a d8 electronic configuration, the tendency is to form a square planar geometry, particularly in certain metal ions such as Nickel(II), Palladium(II), and Platinum(II). These metals prefer this arrangement as it minimizes electron repulsion, and maximizes bonding.

• d8 metals can form stable, low-spin square planar complexes.
• This configuration is quintessential to understanding why some complexes prefer square planar over other geometries.

The square planar geometry also contributes to the unique chemical properties exhibited by these complexes, such as distinct magnetic properties and reactivity patterns.

Transition Metal Complexes

Transition metal complexes are fundamental in understanding inorganic chemistry, given their diverse structures and applications. A transition metal has partially filled d orbitals, and this feature makes it highly versatile in forming complexes with various ligands. These complexes are also pivotal in several industrial and biological processes.

One distinguishing feature of transition metal complexes is their ability to exhibit different geometries based on their oxidation state and electronic configuration. The square planar geometry we often associate with specific transition metals like Platinum(II) and Palladium(II) is a prime example of such diversity.

• Transition metals like Nickel, Palladium, and Platinum can demonstrate varying geometries based on their d electron count.
• The choice of ligands significantly affects the stability and geometry of the complexes.

Understanding transition metal complexes provides insights into the catalytic activities, magnetic properties, and color changes, which are crucial for research and practical applications in various scientific fields.