key term - Low-spin

Definition

Low-spin refers to a state of transition metal complexes where the energy difference between the lower energy and higher energy d-orbitals is significant enough to cause electron pairing in the lower energy orbitals before filling the higher energy orbitals. This phenomenon is often observed in octahedral complexes with strong field ligands that produce a large crystal field splitting, leading to fewer unpaired electrons and often more stable complexes.

5 Must Know Facts For Your Next Test

1. Low-spin configurations are typically found in transition metal complexes with strong field ligands such as CN\(^-\) and CO.
2. The low-spin state generally leads to a decrease in magnetic properties, as there are fewer unpaired electrons compared to high-spin complexes.
3. In an octahedral complex, low-spin situations occur when the crystal field splitting energy (\(\Delta\)) is greater than the pairing energy (P), resulting in electron pairing within the lower energy d-orbitals.
4. The geometry of low-spin complexes is often octahedral or square planar, depending on the metal and its surrounding ligands.
5. Low-spin complexes are usually more stable than their high-spin counterparts due to lower energy configurations and reduced electron repulsion.

Review Questions

• Compare and contrast low-spin and high-spin configurations in transition metal complexes regarding their electron arrangements and magnetic properties.
  • Low-spin configurations result from strong field ligands causing significant crystal field splitting, leading to electron pairing in lower energy d-orbitals before occupying higher energy ones. This typically produces fewer unpaired electrons, resulting in weaker magnetic properties. Conversely, high-spin configurations arise with weak field ligands, allowing electrons to occupy higher energy orbitals first, thus maximizing unpaired electrons and increasing magnetic susceptibility.
• Discuss how crystal field splitting influences whether a transition metal complex will adopt a low-spin or high-spin state.
  • Crystal field splitting plays a crucial role in determining the spin state of a transition metal complex. When the splitting energy (\(\Delta\)) created by strong field ligands exceeds the pairing energy (P), it favors a low-spin state where electrons pair up in lower d-orbitals. On the other hand, if \(\Delta\) is less than P, electrons occupy higher d-orbitals first, leading to a high-spin configuration with more unpaired electrons.
• Evaluate the impact of ligand strength on the stability of low-spin complexes compared to high-spin complexes and its implications for their reactivity.
  • The strength of the ligands directly affects the stability of low-spin complexes. Strong field ligands lead to significant crystal field splitting, promoting a low-spin configuration that results in fewer unpaired electrons and greater stability. This stability generally translates into decreased reactivity, as low-spin complexes are less likely to engage in reactions that involve electron transfer. In contrast, high-spin complexes with weak field ligands possess more unpaired electrons, making them more reactive due to increased electron availability for bonding or redox reactions.

Related terms

Crystal Field Splitting:

The energy difference between the split d-orbitals in a transition metal complex due to the presence of surrounding ligands.

Strong Field Ligands:

Ligands that produce a large crystal field splitting and encourage electron pairing in lower energy d-orbitals.

High-Spin: A state in which electrons occupy higher energy orbitals before pairing occurs, resulting in more unpaired electrons compared to low-spin configurations.