Related Experiment Video
Updated: Jun 7, 2025
Structure and Coordination Determination of Peptide-metal Complexes Using 1D and 2D 1H NMR
Published on: December 16, 2013
Distinguishing between aquo and hydroxo coordination in molecular copper complexes by 1H and 17O ENDOR spectroscopy
Julia Haak1,2, George E Cutsail1,2
1Max Planck Institute for Chemical Energy Conversion, Stiftstraße 34-36, D-45470 Mülheim an der Ruhr, Germany. george.cutsail@cec.mpg.de.
Abstract:
Aquo and hydroxo ligands play an essential role in the chemistry of many copper enzymes and small molecule catalysts. The formation of a series of copper complexes with H2O and OH- ligands in various positions, including [Cu(bpy)(OAc)(H2O)2,ax]+ (Cu-I), [Cu(bpy)(OH)2,eq(HxO)2,ax] (Cu-III), [Cu(OH)4,eq(HxO)2,ax]2- (Cu-IV), [Cu(bpy)(H2O)2,eq(H2O)2,ax]2+ (Cu-V) and [Cu(bpy)2(H2O)ax]2+ (Cu-VI), were investigated through Electron Paramagnetic Resonance (EPR) and UV-Vis spectroscopy in aqueous copper bipyridine solutions in the dependence of the pH and the copper-to-bipyridine ratio (bpy = 2,2'-bipyridine). 2H- and 17O-enrichment of the copper complexes allowed us to determine the 1H and 17O nuclear hyperfine interactions of their HxO ligands via Q-band Electron Nuclear Double Resonance (ENDOR) spectroscopy. These techniques gave direct insight into the metal-ligand covalencies and geometries and were further supported by Density Functional Theory (DFT) calculations. It is shown that 1H and 17O ENDOR spectroscopy can aid in (1) determining the coordination position, thereby differentiating between equatorial and axial HxO ligands and (2) distinguishing equatorial aqua and hydroxo ligands, particularly through their anisotropic dipolar components. We further studied the influence of trans coordinating ligands on the hyperfine parameters of aquo and hydroxo ligands, enabled through contrasting the coordination environments in the examined complexes, supported by quantum chemical computations.
More Related Videos
11:04Ion Mobility-Mass Spectrometry Techniques for Determining the Structure and Mechanisms of Metal Ion Recognition and Redox Activity of Metal Binding Oligopeptides
Published on: September 7, 2019
06:53Author Spotlight: Magnetometric Characterization of Intermediates in the Solid-State Electrochemistry of Redox-Active Metal-Organic Frameworks
Published on: June 9, 2023
Related Concept Videos
03:02Colors and Magnetism
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...
00:56Extraction: Advanced Methods
01:182D NMR: Overview of Heteronuclear Correlation Techniques
02:52Stereoisomerism
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...
01:32UV–Vis Spectroscopy of Conjugated Systems
One of the factors influencing λmax is the extent...
01:192D NMR: Heteronuclear Single-Quantum Correlation Spectroscopy (HSQC)