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Structural Isomerism

Structural Isomerism

Isomerism in Complexes
Isomers are different chemical species that have the same chemical formula. Structural isomerism of coordination compounds can be divided into two subcategories, the linkage isomers and coordination-sphere isomers.
Linkage isomers occur when the coordination compound contains a ligand that can bind to the transition metal center through two different atoms. For example, the CN− ligand can bind through the carbon atom or through the nitrogen atom. Similarly, SCN− can...

Colors and Magnetism

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...

Valence Bond Theory

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...

Valence Bond Theory

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Overview of Valence Bond Theory

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...

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,...

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Related Experiment Video

Updated: Dec 28, 2025

Preparation of SNS CobaltII Pincer Model Complexes of Liver Alcohol Dehydrogenase

Preparation of SNS CobaltII Pincer Model Complexes of Liver Alcohol Dehydrogenase

Published on: March 19, 2020

First Cobalt(II) Spin Crossover Compound with N₄S₂-Donorset.

Fabian Fürmeyer¹, Danny Münzberg¹, Luca M Carrella¹

¹Department of Chemistry, Johannes Gutenberg University Mainz, 55128 Mainz, Germany.

Molecules (Basel, Switzerland)

|February 21, 2020

Summary

Researchers synthesized a novel bis-tridentate 1,3,4-thiadiazole ligand and its iron and cobalt complexes. The cobalt complex exhibits gradual spin crossover (SCO), a first for cobalt(II) with N4S2 coordination.

Keywords:

1,3,4-thiadiazole N4S2-donorset cobalt(II)iron(II)magnetism spin crossover

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Synthesis of Metal Nanoparticles Supported on Carbon Nanotube with Doped Co and N Atoms and its Catalytic Applications in Hydrogen Production

Synthesis of Metal Nanoparticles Supported on Carbon Nanotube with Doped Co and N Atoms and its Catalytic Applications in Hydrogen Production

Published on: December 6, 2021

Area of Science:

Coordination Chemistry
Supramolecular Chemistry
Materials Science

Background:

Development of novel ligands for metal complex synthesis is crucial.
Spin crossover (SCO) materials are of interest for molecular switches and sensors.
N4S2 donor sets offer unique coordination environments for metal ions.

Purpose of the Study:

To synthesize and characterize a novel bis-tridentate 1,3,4-thiadiazole ligand.
To prepare and study mononuclear iron(II) and cobalt(II) complexes using this ligand.
To investigate the spin crossover properties of the synthesized metal complexes.

Main Methods:

Ligand synthesis and characterization (NMR, Mass Spectrometry, Elemental Analysis).
Synthesis and characterization of metal complexes [MII(L)2](ClO4)2 (M = FeII, CoII).
Magnetic susceptibility measurements to determine spin states and SCO behavior.

Main Results:

A novel bis-tridentate 1,3,4-thiadiazole ligand (L) was successfully synthesized.
Two mononuclear complexes, [FeII(L)2](ClO4)2 (C1) and [CoII(L)2](ClO4)2 (C2), were obtained.
Iron(II) complex (C1) is low spin below 300 K. Cobalt(II) complex (C2) exhibits gradual spin crossover (SCO) with T1/2 = 175 K.

Conclusions:

The novel ligand effectively coordinates metal ions in an N4S2 donor set.
The cobalt(II) complex represents the first SCO complex featuring an N4S2 coordination environment.
These findings contribute to the development of new spin crossover materials.