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Related Concept Videos

Valence Bond Theory02:42

Valence Bond Theory

Coordination compounds and complexes exhibit different colors, geometries, and magnetic behavior, depending on the metal atom/ion and ligands from which they are composed. In an attempt to explain the bonding and structure of coordination complexes, Linus Pauling proposed the valence bond theory, or VBT, using the concepts of hybridization and the overlapping of the atomic orbitals. According to VBT, the central metal atom or ion (Lewis acid) hybridizes to provide empty orbitals of suitable...
Spin–Spin Coupling: One-Bond Coupling01:17

Spin–Spin Coupling: One-Bond Coupling

Coupling interactions are strongest between NMR-active nuclei bonded to each other, where spin information can be transmitted directly through the pair of bonding electrons. While nuclei polarize their electrons to the opposite spins, the bonding electron pair has opposite spins. Configurations with antiparallel nuclear spins are expected to be lower in energy. When coupling makes antiparallel states more favorable, J is considered to have a positive value. The one-bond coupling constant, 1J,...
Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)01:22

Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)

Vicinal or three-bond coupling is commonly observed between protons attached to adjacent carbons. Here, nuclear spin information is primarily transferred via electron spin interactions between adjacent C‑H bond orbitals. This generally favors the antiparallel arrangement of spins, so 3J values are usually positive.
The extent of coupling depends on the C‑C bond length, the two H‑C‑C angles, any electron-withdrawing substituents, and the dihedral angle between the involved orbitals. The...
Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)

Two NMR-active nuclei bonded to a central atom can be involved in geminal or two-bond coupling. Geminal coupling is commonly seen between diastereotopic protons in chiral molecules and unsymmetrical alkenes, among others.
The central atom need not be NMR-active because its electrons are affected by the electron polarization of the spin-active atoms. However, spin information is transmitted less effectively than in one-bond coupling, and 2J values are usually weaker than 1J values. The energy of...
Spin–Spin Coupling Constant: Overview01:08

Spin–Spin Coupling Constant: Overview

In bromoethane, the three methyl protons are coupled to the two methylene protons that are three bonds away. In accordance with the n+1 rule, the signal from the methyl protons is split into three peaks with 1:2:1 relative intensities. The methylene protons appear as a quartet, with the relative intensities of 1:3:3:1.
Qualitatively, any spin plus-half nucleus polarizes the spins of its electrons to the minus-half state. Consequently, the paired electron in the hydrogen–carbon bond must have a...
Colors and Magnetism03:02

Colors and Magnetism

Color in Coordination Complexes
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human eye.

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Related Experiment Video

Updated: Jun 2, 2026

Atomic Scale Structural Studies of Macromolecular Assemblies by Solid-state Nuclear Magnetic Resonance Spectroscopy
14:55

Atomic Scale Structural Studies of Macromolecular Assemblies by Solid-state Nuclear Magnetic Resonance Spectroscopy

Published on: September 17, 2017

Structure:function relationships in molecular spin-crossover complexes.

Malcolm A Halcrow1

  • 1School of Chemistry, University of Leeds, Woodhouse Lane, Leeds, UK LS2 9JT. m.a.halcrow@ leeds.ac.uk

Chemical Society Reviews
|April 13, 2011
PubMed
Summary
This summary is machine-generated.

Designing new spin-crossover compounds with specific properties is key for applications. Understanding how material structure influences spin-transition temperature and cooperativity is crucial for crystal engineering.

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Area of Science:

  • Materials Science
  • Solid-State Chemistry
  • Crystallography

Background:

  • Spin-crossover (SCO) compounds are gaining traction for applications in devices, sensors, and soft materials due to their switchable properties like color, magnetism, and conductivity.
  • The rational design of SCO materials with tailored switching characteristics is essential for advancing their practical utility.
  • Crystal engineering of SCO materials necessitates a deep understanding of structure-property relationships, particularly how bulk structure affects spin-transition temperature and cooperativity.

Purpose of the Study:

  • To review molecular spin-crossover compounds with available crystallographic data.
  • To explore the role of molecular shape changes and lattice accommodation in thermal spin-transitions.
  • To provide insights for the de novo design of SCO materials with predictable switching behavior.

Main Methods:

  • Critical review of existing literature on molecular spin-crossover compounds.
  • Analysis of crystallographic data for selected SCO materials.
  • Correlation of structural features with observed spin-transition properties.

Main Results:

  • Emerging understanding highlights the importance of molecular shape changes between high- and low-spin states.
  • The lattice's ability to accommodate these molecular shape changes is a critical factor in spin-transition cooperativity.
  • Structural insights are crucial for predicting and controlling the thermal spin-transition in the solid state.

Conclusions:

  • The interplay between molecular structure, lattice dynamics, and spin-transition behavior is fundamental for SCO materials.
  • Crystal engineering strategies can be informed by understanding how structural factors influence spin-transition cooperativity.
  • This review provides a foundation for designing next-generation SCO materials with targeted applications.