Magnetic Properties of Complex Ions: Videos & Practice Problems

The magnetic properties of transition metal complexes are influenced by crystal field splitting energy. A large splitting results in low spin complexes, where electrons fill lower energy orbitals first, leading to diamagnetic species. Conversely, small splitting creates high spin complexes, allowing electrons to occupy higher energy levels, resulting in paramagnetic species. Square planar geometries are associated with low spin, while tetrahedral geometries correspond to high spin. Understanding these concepts is crucial for predicting the behavior of coordination compounds in various chemical contexts.

Low-Spin Complexes are associated with large Δ values and High-Spin Complexes are associated with small Δ values.

The magnetic properties of transition metal complexes are significantly influenced by the arrangement of their valence electrons in d orbitals, particularly in relation to crystal field splitting energy. This energy difference can be categorized into two types: large crystal field splitting energy and small crystal field splitting energy, which determine whether a complex is classified as low spin or high spin.

In complexes with large crystal field splitting energy, the energy difference between the lower and higher energy d orbitals is substantial. As a result, electrons prefer to occupy the lower energy orbitals first, leading to a low spin complex. For instance, if a metal cation has six electrons, they will fill the lower energy orbitals according to Hund's rule, which states that electrons will fill degenerate orbitals singly before pairing up. In this scenario, all six electrons can be paired in the lower orbitals, resulting in a diamagnetic species, characterized by the absence of unpaired electrons.

The d orbitals are split into two sets: the lower energy set (t₂) consisting of d_xy, d_yz, and d_xz, and the higher energy set (e_g) comprising d_x² - y² and d_z². The energy difference between these sets is referred to as the crystal field splitting energy.

Conversely, in complexes with small crystal field splitting energy, the energy difference between the orbitals is minimal, allowing them to be treated as degenerate. In this case, electrons can easily occupy the higher energy orbitals, resulting in a high spin complex. For the same six electrons, they will fill the lower orbitals first, but due to the small energy difference, they will also occupy the higher orbitals before pairing up. This leads to the presence of unpaired electrons, classifying the complex as paramagnetic.

In summary, the distinction between low spin and high spin complexes is fundamentally linked to the crystal field splitting energy. A large splitting energy favors the formation of low spin complexes with paired electrons, while a small splitting energy promotes high spin complexes with unpaired electrons. Understanding these concepts is crucial for predicting the magnetic behavior of transition metal complexes.

Finding tetrahedral and square planar geometries helps to determine the low vs high spin of complexes.

Understanding the geometries of coordination complexes, specifically tetrahedral and square planar, is crucial for determining their electronic configurations and magnetic properties. In square planar complexes, the crystal field splitting energy, denoted as Δ, is large. This significant energy difference between the two sets of d-orbitals means that electrons prefer to occupy the lower energy orbitals, leading to a configuration where they fill these orbitals before moving to the higher energy ones. As a result, square planar complexes are classified as low spin complexes, which typically exhibit a diamagnetic behavior due to the absence of unpaired electrons in their electron orbital diagrams.

Conversely, tetrahedral complexes are characterized by a smaller Δ, indicating a minimal energy difference between the d-orbitals. In this scenario, the orbitals can be treated as degenerate, meaning they have similar energy levels. Consequently, electrons are more likely to occupy higher energy orbitals, resulting in a high spin configuration. Tetrahedral complexes are generally paramagnetic, as they contain unpaired electrons in their electron orbital diagrams.

In summary, the geometry of a complex significantly influences its spin state: square planar complexes are low spin and diamagnetic, while tetrahedral complexes are high spin and paramagnetic. This relationship is essential when analyzing the properties of various coordination compounds.

Example

To determine the geometry and spin of the complex ion involving palladium, we first establish the oxidation state of palladium. In this case, palladium has a charge of +2, which is necessary to balance the overall charge of the complex, given that there are four bromide ions (each with a charge of -1), contributing a total of -4. Therefore, the palladium ion must be +2 to achieve an overall charge of -2.

Palladium, as a neutral atom, has the electron configuration of krypton (Kr), and due to its unique properties, it does not have electrons in the 5s orbital. Instead, these electrons are promoted to the 4d orbitals, resulting in a configuration of 4d¹⁰. When palladium loses two electrons to form the +2 ion, its configuration becomes 4d⁸.

For a d⁸ configuration, the geometry of the complex ion is typically square planar. This geometry is significant because it influences the crystal field splitting energy. In square planar complexes, the crystal field splitting energy is generally high, leading to low spin configurations. This means that the electrons will pair up in the lower energy orbitals before occupying higher energy orbitals.

Despite the expectation of a low spin complex, it is important to note that palladium is an exception in terms of electron configuration. While square planar complexes are usually diamagnetic, palladium's unique properties can result in unpaired electrons, leading to a paramagnetic orientation. However, in this specific case, we conclude that the complex is square planar and exhibits low spin characteristics.

Determine if the following complex ion is either paramagnetic or diamagnetic: [CoF₄]^2–.

• A. Paramagnetic
• B. Diamagnetic
• C. Cannot be determined

Answer: (A)

Here’s what students ask on this topic:

What determines the magnetic properties of complex ions?

The magnetic properties of complex ions are determined by the crystal field splitting energy (Δ). This energy difference influences whether electrons fill lower or higher energy orbitals first. Large crystal field splitting energy results in low spin complexes where electrons fill lower energy orbitals first, leading to diamagnetic species with paired electrons. Small crystal field splitting energy results in high spin complexes where electrons are more likely to occupy higher energy orbitals, leading to paramagnetic species with unpaired electrons. The geometry of the complex ion, such as square planar or tetrahedral, also plays a role in determining the magnetic properties.

What is the difference between low spin and high spin complexes?

Low spin complexes occur when the crystal field splitting energy (Δ) is large, causing electrons to fill lower energy orbitals first. This results in paired electrons and diamagnetic species. High spin complexes occur when the crystal field splitting energy is small, allowing electrons to occupy higher energy orbitals more easily. This leads to unpaired electrons and paramagnetic species. The geometry of the complex ion, such as square planar or tetrahedral, can influence whether a complex is low spin or high spin.

How does crystal field splitting energy affect electron arrangement in d orbitals?

Crystal field splitting energy (Δ) affects the arrangement of electrons in d orbitals by determining whether electrons fill lower or higher energy orbitals first. In complexes with large Δ, electrons fill lower energy orbitals first, resulting in low spin complexes with paired electrons. In complexes with small Δ, electrons are more likely to occupy higher energy orbitals, leading to high spin complexes with unpaired electrons. The arrangement of electrons in d orbitals influences the magnetic properties of the complex ion.

What are the magnetic properties of square planar and tetrahedral complexes?

Square planar complexes are associated with large crystal field splitting energies (Δ), resulting in low spin complexes with paired electrons. These complexes are typically diamagnetic. Tetrahedral complexes, on the other hand, have small crystal field splitting energies, leading to high spin complexes with unpaired electrons. These complexes are typically paramagnetic. The geometry of the complex ion helps predict its magnetic properties and the arrangement of electrons in its orbitals.

Why are square planar complexes usually diamagnetic?

Square planar complexes are usually diamagnetic because they have a large crystal field splitting energy (Δ). This large energy difference causes electrons to fill the lower energy orbitals first, resulting in paired electrons. Since diamagnetic species have no unpaired electrons, square planar complexes, with their paired electrons, exhibit diamagnetic properties. The large Δ in square planar geometry makes it energetically unfavorable for electrons to occupy higher energy orbitals, leading to a low spin configuration.