Related Experiment Video
Updated: Jul 8, 2026
14:11
Synthesis of pH Dependent Pyrazole, Imidazole, and Isoindolone Dipyrrinone Fluorophores using a Claisen-Schmidt Condensation Approach
Published on: June 10, 2021
Redox-active p-quinone-based Bis(pyrazol-1-yl)methane ligands: synthesis and coordination behaviour
Sebastian Scheuermann1, Tonia Kretz, Hannes Vitze
1Institut für Anorganische und Analytische Chemie, Johann Wolfgang Goethe-Universität Frankfurt am Main, Max-von-Laue-Strasse 7, 60438 Frankfurt, Germany.
Chemistry (Weinheim an Der Bergstrasse, Germany)
|January 12, 2008
Summary
This study introduces novel redox-active p-hydroquinone-based bis(pyrazol-1-yl)methane ligands and their metal complexes. These ligands exhibit reversible redox behavior, paving the way for new applications in catalysis and materials science.
Area of Science:
- Coordination Chemistry
- Organic Synthesis
- Materials Science
Background:
- Development of novel ligands is crucial for advancing coordination chemistry and catalysis.
- Hydroquinone-based ligands offer unique redox properties.
- Bis(pyrazol-1-yl)methane scaffolds are versatile building blocks in supramolecular chemistry.
Purpose of the Study:
- To synthesize and characterize novel mono- and ditopic p-hydroquinone-based bis(pyrazol-1-yl)methane ligands.
- To investigate the coordination behavior of these ligands with transition metals (Ni II and Pd II).
- To explore the redox properties and potential applications of the synthesized ligands and their complexes.
Main Methods:
- Ligand synthesis via established organic chemistry techniques.
- Structural characterization using spectroscopic methods (NMR, IR, Mass Spectrometry) and X-ray crystallography.
- Coordination studies with Ni II and Pd II salts.
- Electrochemical studies to probe redox behavior.
- Preparation and characterization of metal complexes.
Main Results:
- Successful synthesis of four new p-hydroquinone-based bis(pyrazol-1-yl)methane ligands.
- Oxidation of ligands to their p-benzoquinone state, demonstrating preparative scale feasibility.
- Formation of an octahedral Ni II complex and square-planar Pd II complexes.
- Demonstration of fully reversible redox transitions in Pd II complexes, confirmed by the isolation of both reduced and oxidized forms.
- Identification of a highly acidic methine proton in an oxidized Pd II complex, leading to the formation of a dinuclear macrocyclic complex.
- Synthesis of a base-stable methylated ligand and its Pd II complex.
Conclusions:
- A new class of redox-active ligands based on p-hydroquinone bis(pyrazol-1-yl)methane has been developed.
- These ligands exhibit tunable redox properties and form stable complexes with transition metals.
- The reversible redox behavior and structural diversity of the complexes highlight their potential for applications in catalysis and materials science.
Related Concept Videos
02:51Metal-Ligand Bonds
The hemoglobin in the blood, the chlorophyll in green plants, vitamin B-12, and the catalyst used in the manufacture of polyethylene all contain coordination compounds. Ions of the metals, especially the transition metals, are likely to form complexes.
In these complexes, transition metals form coordinate covalent bonds, a kind of Lewis acid-base interaction in which both of the electrons in the bond are contributed by a donor (Lewis base) to an electron acceptor (Lewis acid). The Lewis acid in...
In these complexes, transition metals form coordinate covalent bonds, a kind of Lewis acid-base interaction in which both of the electrons in the bond are contributed by a donor (Lewis base) to an electron acceptor (Lewis acid). The Lewis acid in...
02:57Coordination Number and Geometry
For transition metal complexes, the coordination number determines the geometry around the central metal ion. Table 1 compares coordination numbers to molecular geometry. The most common structures of the complexes in coordination compounds are octahedral, tetrahedral, and square planar.
02:42Valence 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...
02:54Coordination Compounds and Nomenclature
In most main group element compounds, the valence electrons of the isolated atoms combine to form chemical bonds that satisfy the octet rule. For instance, the four valence electrons of carbon overlap with electrons from four hydrogen atoms to form CH4. The one valence electron leaves sodium and adds to the seven valence electrons of chlorine to form the ionic formula unit NaCl (Figure 1a). Transition metals do not normally bond in this fashion. They primarily form coordinate covalent bonds, a...
03:02Colors 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.
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.
02:34Structural 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 be...
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 be...