Related Experiment Video
Updated: Aug 5, 2026
Structure and Coordination Determination of Peptide-metal Complexes Using 1D and 2D 1H NMR
Published on: December 16, 2013
Two types of bridging ligands in dimeric copper(II) complexes with pyrazole derivatives: structure, spectroscopy, and
Małgorzata Zienkiewicz-Machnik1, Roman Luboradzki1, Pavlo Aleshkevych2
1Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland. mzienkiewiczmachnik@ichf.edu.pl.
Abstract:
Two CuII complexes with pyrazole derivatives, [CuL1Cl2]2 (1) and [CuL2(OAc)2]2 (2), have been synthesized and characterized by X-ray crystallography, and spectroscopic (FTIR, UV-Vis, and EPR) and magnetic methods supported by quantum chemical calculations. Crystallographic measurements revealed that both complexes exhibit a dimeric structure with five-coordinated metal centres and square pyramidal geometry. Copper ions in complex 1 are linked by a double chloride bridge, while in 2, the presence of four bridged acetate ligands supports the paddle-wheel structure. Variable temperature magnetic susceptibility measurements established an antiferromagnetic interaction between the CuII centres in both complexes: very weak in 1 and very strong in 2. Moreover, the experimentally obtained J values for both complexes agreed perfectly with the calculated ones. Both complexes are soluble in MeOH, CH3CN, and DMSO, and this property has been exploited to investigate the solvent effect on catecholase activity. The complexes are active in the tested reaction across all tested solvents, exhibiting a typical first-order dependence at low substrate concentrations. Moreover, a kinetic study on catecholase activity revealed a significant impact of the solvent on catalytic activity, especially in the case of complex 2, where an inhibition process occurs at higher substrate concentrations in CH3CN, which is unusual for metal complexes tested in this reaction, as they typically follow zero-order saturation kinetics. Furthermore, a comparison of the EPR spectra of the solid complexes and their MeOH solutions, and quantum chemical calculation results showed that both complexes undergo significant changes in their nature in solution, excluding symmetric cleavage to the respective monomers.
Related Concept Videos
02:51Metal-Ligand Bonds
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...
00:43Complexometric Titration: Ligands
01:22EDTA: Chemistry and Properties
02:58Crystal Field Theory - Octahedral Complexes
To explain the observed behavior of transition metal complexes (such as colors), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory (CFT). It helps to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.
CFT focuses on...
02:34Structural Isomerism
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...
01:19Complexation Equilibria: The Chelate Effect