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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)

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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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Spin–Spin Coupling: One-Bond Coupling01:17

Spin–Spin Coupling: One-Bond Coupling

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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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Stereoisomerism of Cyclic Compounds02:33

Stereoisomerism of Cyclic Compounds

9.2K
In this lesson, we delve into the role of ring conformation and its stability, which determines the spatial arrangement and, consequently, the molecular symmetry and stereoisomerism of cyclic compounds. 1,2-Dimethylcyclohexane is used as a case study to evaluate the possible number of stereoisomers. Here, given the multiple (n = 2) chiral centers, there are 2n = 4 possible configurations that lack a plane of symmetry, as the ring skeleton exists in a non-planar chair conformation. In addition,...
9.2K
SN2 Reaction: Stereochemistry02:23

SN2 Reaction: Stereochemistry

9.8K
In an SN2 reaction, the nucleophilic attack on the substrate and departure of the leaving group occurs simultaneously through a transition state. As the nucleophile approaches the substrate from the back-side, the configuration of the substrate carbon changes from tetrahedral to trigonal bipyramidal and then back to tetrahedral, leading to an inversion in the configuration of the product.
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Stereoisomerism02:52

Stereoisomerism

11.1K
Isomerism in Complexes
Isomers are different chemical species that have the same chemical formula.
Transition metal complexes often exist as geometric isomers, in which the same atoms are connected through the same types of bonds but with differences in their orientation in space. Coordination complexes with two different ligands in the cis and trans positions from a ligand of interest form isomers. For example, the octahedral [Co(NH3)4Cl2]+ ion has two isomers (Figure 1) In the cis...
11.1K
Spin–Spin Coupling: Three-Bond Coupling (Vicinal Coupling)01:22

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

1.3K
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...
1.3K

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Molecular Entanglement and Electrospinnability of Biopolymers
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Spin-crossover behavior in two new supramolecular isomers.

Zheng Yan1, Zhao-Ping Ni, Fu-Sheng Guo

  • 1Key Laboratory of Bioinorganic and Synthetic Chemistry of Ministry of Education, State Key Laboratory of Optoelectronic Materials and Technologies, School of Chemistry and Chemical Engineering, Sun Yat-Sen University , 135 Xingang Road West, Guangzhou 510275, P. R. China.

Inorganic Chemistry
|December 24, 2013
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Summary

Two novel spin-crossover supramolecular isomers were synthesized and characterized. Their distinct structures, a 2D coordination layer and a 1D ladder, influence the iron(II) spin transition properties.

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Area of Science:

  • Coordination Chemistry
  • Materials Science
  • Supramolecular Chemistry

Background:

  • Spin-crossover (SCO) materials exhibit a reversible switch between low-spin and high-spin states.
  • The structural and electronic properties of SCO complexes are crucial for tuning their transition temperatures.
  • Supramolecular isomers offer a unique platform to investigate structure-property relationships in SCO systems.

Purpose of the Study:

  • To synthesize and characterize two distinct supramolecular isomers of a spin-crossover iron(II) complex.
  • To elucidate the influence of structural dimensionality and ligand coordination modes on SCO behavior.
  • To correlate structural features with observed spin transition temperatures and mechanisms.

Main Methods:

  • Single-crystal X-ray crystallography for structural determination.
  • Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) for thermal properties.
  • Variable-temperature powder X-ray diffraction (VT-PXRD) and magnetic susceptibility measurements for SCO characterization.

Main Results:

  • Two supramolecular isomers, a 2D coordination layer (1) and a 1D coordination ladder (2·H2O), were successfully isolated.
  • Ligand coordination (trans vs. cis bridging) differed between the isomers, influencing the Fe(II) octahedral environment.
  • Isomer 1 showed SCO at 303 K (trans Fe(II)), while 2·H2O exhibited gradual two-step SCO (235 K and 313 K) and dehydrated 2 showed one-step SCO (315 K).

Conclusions:

  • The structural dimensionality and coordination geometry significantly impact the spin-crossover properties of the iron(II) complexes.
  • Supramolecular isomerism provides a powerful strategy to fine-tune SCO behavior.
  • These findings contribute to the design of advanced functional materials with switchable magnetic properties.