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Complexation Equilibria: The Chelate Effect

Complexation Equilibria: The Chelate Effect

In complexation reactions, metal atoms or cations interact with ligands to form donor-acceptor adducts called metal complexes. Ligands that bind through one donor site are monodentate, ligands with two donor sites are bidentate, and those with more than two donor sites are polydentate ligands. For example, ethylene diamine is a bidentate ligand that binds through two nitrogen donor atoms, forming a five-membered ring. EDTA is a polydentate ligand that binds through four oxygen and two nitrogen...

Metal-Ligand Bonds

Metal-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...

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...

Crystal Field Theory - Octahedral Complexes

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Crystal Field Theory
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...

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 eye.

Crystal Field Theory - Tetrahedral and Square Planar Complexes

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Tetrahedral Complexes
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...

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Iridium(III) Luminescent Probe for Detection of the Malarial Protein Biomarker Histidine Rich Protein-II

Iridium(III) Luminescent Probe for Detection of the Malarial Protein Biomarker Histidine Rich Protein-II

Published on: July 7, 2015

Light-emitting iridium complexes with tridentate ligands.

J A Gareth Williams¹, Andrew J Wilkinson, Victoria L Whittle

¹Department of Chemistry, University of Durham, Durham, UKDH1 3LE. j.a.g.williams@durham.ac.uk

Dalton Transactions (Cambridge, England : 2003)

|April 10, 2008

Summary

This summary is machine-generated.

Iridium(III) complexes with tridentate ligands exhibit tunable luminescence. The number of cyclometallating carbon atoms significantly impacts luminescence efficiency, offering a wide range of applications in photochemistry.

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Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene

Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene

Published on: March 20, 2017

Area of Science:

Inorganic Chemistry
Photochemistry
Materials Science

Background:

Iridium(III) complexes have gained significant attention for their luminescent properties.
While tris-bidentate iridium complexes are well-studied, tridentate ligands offer a diverse chemical landscape.
Understanding structure-property relationships is crucial for optimizing luminescence.

Purpose of the Study:

To review the synthesis and excited-state properties of iridium(III) complexes with tridentate ligands.
To investigate the influence of cyclometallating carbon atoms on luminescence.
To rationalize luminescence differences based on molecular structure and frontier orbitals.

Main Methods:

Synthesis of various iridium(III) complexes with varying numbers of cyclometallating ligands.
Characterization of excited-state properties, including luminescence efficiency and emission wavelengths.
Computational analysis of frontier orbitals to correlate with observed luminescence.

Main Results:

A wide range of luminescence efficiencies were observed, from near-undetectable to quantum yields approaching unity.
Tuning the number of cyclometallating carbon atoms in the coordination sphere profoundly affects luminescence.
Subtle molecular structure changes lead to significant differences in photophysical behavior.

Conclusions:

Tridentate iridium(III) complexes offer versatile platforms for tunable luminescence.
The degree of cyclometallation is a key factor in controlling luminescence efficiency.
Frontier orbital analysis provides insights into the observed structure-property relationships for these luminescent materials.