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Related Concept Videos

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

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The spin state of an NMR-active nucleus can have a slight effect on its immediate electronic environment. This effect propagates through the intervening bonds and affects the electronic environments of NMR-active nuclei up to three bonds away; occasionally, even farther. This phenomenon is called spin–spin coupling or J-coupling. Coupling interactions are mutual and result in small changes in the absorption frequencies of both nuclei involved. While nuclei of the same element are involved in...
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Hyperpolarized 13C Metabolic Magnetic Resonance Spectroscopy and Imaging
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Antagonism between extreme negative linear compression and spin crossover in [Fe(dpp)(2)(NCS)(2)]⋅py.

Helena J Shepherd1, Tatiana Palamarciuc, Patrick Rosa

  • 1Laboratoire de Chimie de Coordination, CNRS UPR, Toulouse, France.

Angewandte Chemie (International Ed. in English)
|March 13, 2012
PubMed
Summary

A novel scissor-like mechanism in a molecular material causes unprecedented negative linear compression. This geometric effect also prevents pressure-induced spin transitions in the iron complex.

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Area of Science:

  • Materials Science
  • Solid-State Chemistry
  • Molecular Engineering

Background:

  • Negative linear compression (NLC) is a rare phenomenon where a material contracts along one dimension when stretched along another.
  • Understanding the mechanisms behind NLC is crucial for designing advanced materials with unique mechanical properties.
  • Iron(II) spin crossover (SCO) complexes offer tunable electronic and magnetic properties sensitive to external stimuli like pressure.

Purpose of the Study:

  • To investigate the structural and mechanical response of the molecular material [Fe(dpp)(2)(NCS)(2)]⋅py under pressure.
  • To elucidate the geometric mechanism responsible for the observed negative linear compression.
  • To understand the interplay between the NLC mechanism and the spin crossover behavior of the iron complex.

Main Methods:

  • Single-crystal X-ray diffraction under hydrostatic pressure.
  • Variable-temperature magnetic susceptibility measurements.
  • Rietveld refinement of powder X-ray diffraction data.

Main Results:

  • Observed the strongest negative linear compression effect reported to date in a molecular material, reaching -3.5% strain.
  • Identified a scissor-like geometric mechanism involving the [Fe(dpp)(2)(NCS)(2)]⋅py structure that drives the NLC.
  • Demonstrated that this mechanism suppresses the high-spin to low-spin transition of the iron(II) center up to 1.5 GPa.

Conclusions:

  • The scissor-like geometric mechanism is the origin of the record-breaking negative linear compression in [Fe(dpp)(2)(NCS)(2)]⋅py.
  • This mechanism effectively decouples the structural response from the spin crossover transition, highlighting a new pathway for controlling SCO behavior.
  • The findings open avenues for designing molecular materials with tailored mechanical and electronic properties for advanced applications.