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Related Concept Videos

Valence Bond Theory02:42

Valence Bond Theory

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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...
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Complexation Equilibria: Factors Influencing Stability of Complexes01:09

Complexation Equilibria: Factors Influencing Stability of Complexes

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In complexation reactions, metal cations are the electron pair acceptors, and the ligands are the electron pair donors. The stability of the metal complexes depends primarily on the complexing ability of the central metal ion and the nature of the ligands. Generally, the complexing ability of the metal ion depends on the size and charge of the ion. As the metal ion size increases, the stability of the metal complexes decreases, provided that the valency of the metal ion and the ligands remain...
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Structural Isomerism02:34

Structural Isomerism

19.5K
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...
19.5K
Colors and Magnetism03:02

Colors and Magnetism

12.0K
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...
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Complexation Equilibria: The Chelate Effect01:19

Complexation Equilibria: The Chelate Effect

564
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...
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ortho–para-Directing Activators: –CH3, –OH, –⁠NH2, –OCH301:11

ortho–para-Directing Activators: –CH3, –OH, –⁠NH2, –OCH3

6.1K
All ortho–para directors, excluding halogens, are activating groups. These groups donate electrons to the ring, making the ring carbons electron-rich. Consequently, the reactivity of the aromatic ring towards electrophilic substitution increases. For instance, the nitration of anisole is about 10,000 times faster than the nitration of benzene. The electron-donating effect of the methoxy group in anisole activates the ortho and para positions on the ring and stabilizes the corresponding...
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Preparation of 6-aminocyclohepta-2,4-dien-1-one Derivatives via Tricarbonyltroponeiron
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Enabling Valence Delocalization in Iron(III) Macrocyclic Complexes through Ring Unsaturation.

Reese A Clendening1, Stephanie S Delancey1, Andrew T Poore1

  • 1Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States.

Inorganic Chemistry
|June 30, 2023
PubMed
Summary
This summary is machine-generated.

The tetra-imino macrocycle HMTI promotes significant valence delocalization in iron complexes, unlike the tetra-aza macrocycle HMC. This difference in electronic structure influences electron delocalization and metal-orbital energies.

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Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene
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Characterizing Lewis Pairs Using Titration Coupled with In Situ Infrared Spectroscopy
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Characterizing Lewis Pairs Using Titration Coupled with In Situ Infrared Spectroscopy
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Area of Science:

  • Coordination Chemistry
  • Organometallic Chemistry
  • Spectroelectrochemistry

Background:

  • Iron complexes with macrocyclic ligands are crucial in various chemical and biological systems.
  • Understanding electron delocalization in mixed-valent metal complexes is key to designing advanced materials.
  • The electronic properties of macrocyclic ligands significantly influence metal center reactivity and redox behavior.

Purpose of the Study:

  • To synthesize and characterize novel iron(III) complexes with tetra-imino (HMTI) and tetra-aza (HMC) macrocyclic ligands.
  • To investigate the effect of macrocyclic ligand structure on valence delocalization in mixed-valent iron species.
  • To elucidate the role of ligand π-acidity in modulating electronic communication within the complexes.

Main Methods:

  • Synthesis and full characterization of iron(III) complexes [Fe(HMC)(C2DMA)2]CF3SO3 and [Fe(HMTI)(C2Y)2]CF3SO3.
  • Vibrational and electronic absorption spectroelectrochemical analyses to study one-electron oxidation.
  • Electron paramagnetic resonance (EPR) and Mössbauer spectroscopy to probe electronic structure and metal properties.

Main Results:

  • Significant valence delocalization was observed in HMTI-based complexes due to the tetra-imino macrocycle.
  • Mixed-valent ions derived from the HMC-based complex exhibited more localized electronic character.
  • The π-acidity of HMTI lowers Fe(III) dπ orbital energies compared to the σ-donating HMC ligand.

Conclusions:

  • The tetra-imino macrocycle HMTI facilitates substantial valence delocalization across the -C2-FeIII-C2- bridge.
  • Macrocycle-dependent valence delocalization is strongly influenced by ligand π-acidity and σ-donation.
  • These findings provide insights into controlling electronic communication in iron-based molecular materials.