Question

The complex ion \(\mathrm{PdCl}_{4}^{2-}\) is diamagnetic. Propose a structure for \(\mathrm{PdCl}_{4}^{2-}\).

Short answer

The structure of the complex ion \(\mathrm{PdCl}_{4}^{2-}\) is square planar, with the Pd(II) ion at the center and the 4 Cl- ions surrounding it. This geometry allows all electrons to be paired up, making the complex diamagnetic.

Step-by-step solution

Determine the electron configuration of Pd

Pd is a palladium ion, which is in the 5th period and 10th group of the periodic table. Its atomic number is 46, so its ground state electron configuration is [Kr] 4d^10 5s^0.

Calculate the charge of Pd ion in the complex

The complex ion given is \(\mathrm{PdCl}_{4}^{2-}\). The total charge of the complex is -2. Chlorine ions (Cl-) have a charge of -1 each. Since there are 4 Cl- ions in the complex, Pd must have a charge of +2 in order to ensure that the overall charge of the complex ion is -2.

Determine the electron configuration of Pd(II)

We now know that the Pd ion has a charge of +2. In order to achieve the +2 charge, Pd must lose 2 electrons from its valence shell. In this case, Pd(II) will have an electron configuration of [Kr] 4d^8 5s^0.

Determine the coordination number and structure

A diamagnetic complex has all electrons in the complex ion paired up. We know that for \(\mathrm{PdCl}_{4}^{2-}\), there are 4 Cl- ligands surrounding the Pd(II) ion. Considering that Cl- is a monodentate ligand (coordinating through a single coordinate covalent bond), the coordination number for Pd(II) is 4.

Identify geometry

Coordination complexes with a coordination number of 4 typically exhibit one of two geometries: tetrahedral or square planar. Since \(\mathrm{PdCl}_{4}^{2-}\) is diamagnetic and Pd(II) has an electron configuration of [Kr] 4d^8 5s^0, a square planar geometry would allow all electrons to be paired up in the complex ion.

Propose structure

Given the information that we have about the complex ion \(\mathrm{PdCl}_{4}^{2-}\) being diamagnetic and having a coordination number of 4, the proposed structure for this complex ion is a square planar geometry with the Pd(II) ion at the center and the 4 Cl- ions surrounding it.

Key concepts

Diamagnetism

Diamagnetism is a property of materials where all the electrons are paired, leading to no net magnetic moment. This means that such materials are not attracted to a magnetic field, and may even be slightly repelled.

In coordination chemistry, the magnetic properties of complex ions can help determine their electronic configuration and geometry. For example, a known diamagnetic complex will have all its electrons paired. This aligns with the observation that the \(\mathrm{PdCl}_{4}^{2-}\) complex is diamagnetic, suggesting a configuration where all electrons are paired, particularly fitting a square planar geometry.

Recognizing the diamagnetic nature of a compound is essential in predicting its behavior in magnetic fields and its electronic distribution.

Complex Ions

Complex ions are formed when central metal atoms or ions bind with surrounding molecules or ions, known as ligands. These bonds are coordinate covalent bonds, where both electrons in the bond come from the ligand.

In the example of \(\mathrm{PdCl}_{4}^{2-}\), palladium (Pd) acts as the central metal ion, coordinated by four chloride ions (Cl\(^-\)) that serve as the ligands.

The formation of complex ions is key in understanding their structures and properties such as magnetic behavior and geometric arrangements. The stability, color, and reactivity of a complex ion are deeply influenced by the nature of the metal and ligands in it.

• The central metal: Often a transition metal, providing d orbitals for bonding.
• Ligands: Molecules or ions surrounding the metal, influencing the complex's properties.

Electron Configuration

Electron configuration is a notation that shows the distribution of electrons among the orbitals of an atom or ion. It helps predict and explain the chemical and physical properties of elements and their ions.

For palladium (Pd), the electron configuration is particularly interesting because it places its electrons in the d orbitals. Initially, the ground state electron configuration for Pd is [\mathrm{Kr}] 4d^{10} 5s^0.

When Pd forms a +2 oxidation state in \(\mathrm{PdCl}_{4}^{2-}\), it loses two electrons from its outer shell, leading to the electron configuration [\mathrm{Kr}] 4d^8 5s^0.

• Ground state configuration: Indicates the electron filling order.
• Ion formation: Involves loss or gain of electrons, affecting configuration.

Coordination Number

The coordination number of a complex ion is the number of ligand atoms that are directly bonded to the central metal ion. This number is crucial in determining the geometric structure of the complex.

In \(\mathrm{PdCl}_{4}^{2-}\), the coordination number is 4 because there are four chloride ions directly attached to the central palladium ion.

Knowing the coordination number helps predict the geometry that the complex will adopt. A coordination number of 4 usually leads to either a tetrahedral or square planar geometry, but factors like the metal's electronic configuration will influence the final structure.

Square Planar Geometry

Square planar geometry is one of the geometric arrangements seen in coordination chemistry, particularly for complexes with a coordination number of 4.

In a square planar geometry, the ligands are arranged at the corners of a square with the central metal ion at the center.

This geometry is often observed in complexes with d\(^{8}\) electron configurations, like \(\mathrm{PdCl}_{4}^{2-}\). The arrangement allows for the stabilization of the electronic configuration and pairing of all electrons, facilitating diamagnetism.

• Arrangement: Ligands at the corners forming a square.
• Common for: d\(^{8}\) metals and metals forming low-spin configurations.
• Effect: Stabilizes the complex by efficient electron pairing.