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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: 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: 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...
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.
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...

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High-Temperature and High-Pressure In situ Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopy
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High-Temperature and High-Pressure In situ Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopy

Published on: October 9, 2020

High-pressure spin-crossover in a dinuclear Fe(II) complex.

Helena J Shepherd1, Patrick Rosa, Laure Vendier

  • 1Laboratoire de Chimie de Coordination, CNRS UPR-8241, and Université de Toulouse, UPS, INP, Toulouse, France.

Physical Chemistry Chemical Physics : PCCP
|March 10, 2012
PubMed
Summary
This summary is machine-generated.

Pressure-induced spin crossover in a dinuclear iron complex reveals a complete low-spin state, distinct from thermal transitions. This behavior, observed without crystallographic phase changes, highlights pressure

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Area of Science:

  • Materials Science
  • Inorganic Chemistry
  • Solid-State Physics

Background:

  • Spin crossover (SCO) materials exhibit distinct high-spin and low-spin states.
  • Dinuclear iron complexes are of interest for their cooperative SCO properties.
  • Understanding external stimuli effects, like pressure, is crucial for SCO material applications.

Purpose of the Study:

  • To investigate the effect of pressure on the spin crossover behavior of a specific dinuclear iron complex.
  • To compare pressure-induced SCO with thermally induced SCO in the same material.
  • To elucidate the structural changes accompanying pressure-driven spin transitions.

Main Methods:

  • Single crystal X-ray diffraction under high pressure using diamond anvil cell.
  • Raman spectroscopy under high pressure using diamond anvil cell.
  • Synthesis and characterization of the dinuclear iron complex [{Fe(bpp)(NCS)(2)}(2)(4,4'-bipy)]·2MeOH.

Main Results:

  • A gradual, pressure-induced spin crossover was observed between 7 and 25 kbar.
  • The pressure-induced transition leads to a complete low-spin (LS) state, not achievable thermally.
  • No crystallographic phase transitions were detected during the pressure-induced SCO, contrasting with thermal behavior.

Conclusions:

  • Pressure can induce a complete LS state in this dinuclear iron complex, which is inaccessible via thermal means.
  • The absence of a symmetry-breaking phase transition under pressure is key to achieving the full LS state.
  • This study demonstrates distinct pressure-dependent SCO mechanisms compared to thermal pathways in dinuclear SCO materials.