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Related Concept Videos

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.
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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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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.
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Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)01:22

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Cycloadditions are one of the most valuable and effective synthesis routes to form cyclic compounds. These are concerted pericyclic reactions between two unsaturated compounds resulting in a cyclic product with two new σ bonds formed at the expense of π bonds. The [4 + 2] cycloaddition, known as the Diels–Alder reaction, is the most common. The other example is a [2 + 2] cycloaddition.
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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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Macrocycle-based spin-crossover materials.

Fatima El Hajj1, Ghania Sebki, Véronique Patinec

  • 1UMR CNRS 6521, Chimie, Electrochimie Moleculaires, Chimie Analytique, Université de Bretagne Occidentale, BP 809, 29285 Brest Cedex, France.

Inorganic Chemistry
|September 29, 2009
PubMed
Summary
This summary is machine-generated.

Researchers synthesized novel iron(II) complexes with tetraazamacrocycles, revealing distinct geometries and spin states. Complex 2 exhibits a spin-crossover transition, with structural changes impacting lattice parameters.

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Area of Science:

  • Coordination Chemistry
  • Inorganic Chemistry
  • Materials Science

Background:

  • Iron(II) complexes with macrocyclic ligands are crucial in catalysis and spin-crossover phenomena.
  • Understanding ligand effects on metal ion coordination geometry and spin states is key to designing functional materials.

Purpose of the Study:

  • To synthesize and characterize new iron(II) complexes with functionalized tetraazamacrocycles.
  • To investigate the structural, magnetic, and spin-crossover properties of these complexes.
  • To correlate structural changes with magnetic transitions.

Main Methods:

  • Infrared spectroscopy for characterization.
  • Variable-temperature single-crystal X-ray diffraction to determine crystal structures.
  • Variable-temperature magnetic susceptibility measurements to assess magnetic behavior and spin states.

Main Results:

  • Two iron(II) complexes, [Fe(L1)](BF(4))(2) and [Fe(L2)](BF(4))(2) x H(2)O, were synthesized.
  • Complex 1 displays a distorted trigonal prismatic geometry for Fe(II) in a high-spin state.
  • Complex 2 shows a distorted octahedral geometry, exhibiting a spin-crossover transition from high-spin to low-spin states, with significant lattice parameter changes upon cooling.

Conclusions:

  • The synthesized iron(II) complexes exhibit diverse coordination geometries and spin behaviors.
  • Complex 2 demonstrates a spin-crossover transition influenced by macrocyclic ligand constraints, leading to notable changes in crystal lattice parameters.
  • These findings contribute to the understanding of spin-crossover mechanisms in iron complexes.