H

High-Spin Complex

High-spin: weak field ligand, max unpaired e⁻; Δ_oct < pairing energy
Quick Reference
Formula / NotationHigh-spin: weak field ligand, max unpaired e⁻; Δ_oct < pairing energy
Also Known AsHigh-spin configuration, weak field complex, outer orbital complex (older term)

What is High-Spin Complex?

A coordination complex in which the crystal field splitting energy is smaller than the pairing energy, causing electrons to occupy all d-orbitals singly before pairing occurs. High-spin complexes have the maximum number of unpaired electrons and are typically formed with weak-field ligands.

Formula & Notation

High-spin: weak field ligand, max unpaired e⁻; Δ_oct < pairing energy

Other Names / Synonyms: High-spin configuration, weak field complex, outer orbital complex (older term)

Properties & Characteristics

A high-spin complex is a transition metal coordination complex in which the crystal field splitting energy (Δ_oct for octahedral) is smaller than the electron pairing energy. As a result, electrons occupy all five d orbitals (including the higher-energy eg) before pairing, following Hund's rule, maximising the number of unpaired electrons. High-spin complexes typically have weak field ligands (F⁻, Cl⁻, Br⁻, I⁻, H₂O) in the spectrochemical series.

Uses & Applications

High-spin vs. low-spin determination is important in: explaining magnetic properties of coordination compounds (high-spin Fe³⁺ has 5 unpaired electrons, is paramagnetic), understanding enzyme active sites (high-spin Fe²⁺ in deoxy-haemoglobin becomes low-spin on O₂ binding, causing the structural change that triggers cooperativity), and in inorganic synthesis design.

Safety Information

High-spin metal complexes with paramagnetic centres may interfere with MRI contrast agent applications (competing signals). Safety considerations are those of the specific metal ion and ligands involved in the complex.

Always consult the SDS/MSDS before handling any chemical. This information is for educational purposes only.

Key Facts

Term High-Spin Complex
Formula High-spin: weak field ligand, max unpaired e⁻; Δ_oct < pairing energy
Synonyms High-spin configuration, weak field complex, outer orbital complex (older term)

Frequently Asked Questions

A coordination complex in which the crystal field splitting energy is smaller than the pairing energy, causing electrons to occupy all d-orbitals singly before pairing occurs. High-spin complexes have the maximum number of unpaired electrons and are typically formed with weak-field ligands.

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