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Spin–Spin Coupling Constant: Overview

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...

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

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...

¹H NMR: Complex Splitting

¹H NMR: Complex Splitting

A proton M that is coupled to a proton X results in doublet signals for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When M is coupled to a second proton A, such as in styrene oxide, each peak in the doublet is split into another doublet.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied...

¹H NMR: Interpreting Distorted and Overlapping Signals

¹H NMR: Interpreting Distorted and Overlapping Signals

Spin systems where the difference in chemical shifts of the coupled nuclei is greater than ten times J are called first-order spin systems. These nuclei are weakly coupled, and their chemical shifts and coupling constant can generally be estimated from the well-separated signals in the spectrum.
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are...

Spin–Spin Coupling: One-Bond Coupling

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)

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...

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Probe Type II Band Alignment in One-Dimensional Van Der Waals Heterostructures Using First-Principles Calculations

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Binuclear spin-crossover [Fe(bt)(NCS)₂]₂(bpm) complex: A study using first principles calculations.

Koussai Lazaar¹, Fatma Aouaini², Saber Gueddida³

¹Université Paris-Saclay, Université Evry, CNRS, LAMBE UMR8587, 91025 Evry-Courcouronnes, France.

The Journal of Chemical Physics

|April 15, 2023

Summary

This study investigates the spin-crossover iron complex [Fe(bt)(NCS)2]2(bpm), revealing three magnetic configurations. These configurations align with experimental observations at two distinct transition temperatures, confirming antiferromagnetic coupling in the high-spin state.

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Area of Science:

Computational Chemistry
Materials Science
Solid-State Physics

Background:

Spin-crossover (SCO) complexes exhibit distinct magnetic states.
Understanding the magnetic coupling and transitions in binuclear SCO complexes is crucial for materials design.

Purpose of the Study:

To computationally investigate the spin-crossover behavior of the [Fe(bt)(NCS)2]2(bpm) complex.
To determine the magnetic configurations and coupling between iron centers.
To correlate theoretical findings with experimental transition temperatures.

Main Methods:

Spin-polarized density functional theory (DFT) with generalized gradient approximation (GGA).
Inclusion of Hubbard U and weak van der Waals interactions.
Projector augmented wave (PAW) method in both molecular and periodic arrangements.

Main Results:

Identified three magnetic configurations: high spin-high spin (HS-HS), high spin-low spin (HS-LS), and low spin-low spin (LS-LS).
Observed antiferromagnetic coupling between the two Fe centers in the HS-HS state for both molecular and periodic structures.
Calculated energy differences between magnetic states are smaller than those in related mononuclear or binuclear compounds.

Conclusions:

The theoretical model accurately reproduces the experimentally observed magnetic configurations and transition temperatures (163 K and 197 K).
The study confirms the antiferromagnetic coupling in the HS-HS state, consistent with experimental data.
The findings highlight the computational efficiency and accuracy of the employed DFT methods for SCO complex studies.