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Related Concept Videos

Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)01:20

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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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Electrocyclic reactions, cycloadditions, and sigmatropic rearrangements are concerted pericyclic reactions that proceed via a cyclic transition state. These reactions are stereospecific and regioselective. The stereochemistry of the products depends on the symmetry characteristics of the interacting orbitals and the reaction conditions. Accordingly, pericyclic reactions are classified as either symmetry-allowed or symmetry-forbidden. Woodward and Hoffmann presented the selection criteria for...
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Spin–Spin Coupling: One-Bond Coupling01:17

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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,...
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[3,3] Sigmatropic Rearrangement of 1,5-Dienes: Cope Rearrangement01:21

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The Cope rearrangement is classified as a [3,3] sigmatropic shift in 1,5-dienes, leading to a more stable, isomeric 1,5-diene. The reaction involves a concerted movement of six electrons, four from two π bonds and two from a σ bond, via an energetically favorable chair-like transition state.
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Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)01:22

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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.
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Valence Bond Theory02:42

Valence Bond Theory

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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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Line Shape Analysis of Dynamic NMR Spectra for Characterizing Coordination Sphere Rearrangements at a Chiral Rhenium Polyhydride Complex
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Hysteretic Two-Step Spin-Crossover Behavior in Two Two-Dimensional Hofmann-Type Coordination Polymers.

Fu-Ling Liu1, Jun Tao1,2

  • 1Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, 361005, Fujian, P. R. China.

Chemistry (Weinheim an Der Bergstrasse, Germany)
|October 19, 2017
PubMed
Summary

Two new coordination polymers (CPs) exhibit cooperative spin crossover (SCO) behavior. These materials display two distinct SCO steps, influenced by structural interactions within their 2D layers.

Keywords:
Hofmann-type structureshysteresisiron(II)phase transitionsspin crossover

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Area of Science:

  • Materials Chemistry
  • Coordination Polymers
  • Spin Crossover Materials

Background:

  • Hofmann-like coordination polymers (CPs) are investigated for their unique structural and electronic properties.
  • Spin crossover (SCO) in metal-organic frameworks offers potential for stimuli-responsive applications.

Purpose of the Study:

  • To synthesize and characterize novel 2D coordination polymers based on ferrous salts and tetracyanometallates.
  • To investigate the spin crossover behavior and structural transitions in the newly formed CPs.

Main Methods:

  • Synthesis of coordination polymers using ferrous salts, [MII(CN)4]2- (M=Pd, Pt), and 4-(1H-pyrazol-3-yl)pyridine (Hppy).
  • Variable-temperature single-crystal X-ray crystallography.
  • Differential scanning calorimetry (DSC) and magnetic measurements.

Main Results:

  • Formation of two isostructural 2D Hofmann-like CPs: {FeII(Hppy)2[MII(CN)4]}⋅H2O (M=Pd, Pt).
  • Both CPs exhibit cooperative, complete spin crossover with two distinct steps and hysteresis.
  • SCO cooperativity is attributed to hydrogen bonds and π⋅⋅⋅π interactions, accompanied by phase transitions.

Conclusions:

  • The synthesized coordination polymers demonstrate complex spin crossover phenomena.
  • Structural features, including hydrogen bonding and π-stacking, play a crucial role in the cooperative SCO behavior.
  • The observed two-step SCO transitions are linked to accompanying phase transitions, highlighting their potential for advanced materials.