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Fig.1. Redox innocent ligand

Fe^III-TAML Complexes General Features:

Iron(III) TAMLs are highly active catalysts that function effectively at very low concentrations. These catalysts remain fairly stable under catalytic conditions such that they are capable of achieving high turnover numbers. Fe-TAML activators catalyze the chemistry of a variety of peroxides. The reactions typically take place at room temperature under ambient conditions, however, they are pH dependent. The catalysts have high reactivity rates under basic conditions. Fe-TAML catalysts use hydrogen peroxide to oxidize a broad range of substrates, exhibiting very high reactivity. TAML activators have proven to be highly effective mimics of peroxidases and cytochrome P450 oxidizing enzymes. These catalysts are typically used for purifying water and have been proven to be very effective in doing so.

Fig. 2. Redox non-innocent ligand

Structure in Solid-State:

From the x-ray structures, Fe(III)-TAML complexes are shown to be five-coordinated in solid state. The structure has either an axial chloride or an axial water. The structure typically has a high degree of planarity with all the amide nitrogens lying in the same plane and the Fe located out of the amide plane, towards the axial ligand. This displacement is higher for axial chloride compared to axial water. Typically, these complexes show short average equatorial bond distances of Fe-N, and long axial bonds.

Structure in Solution:

EPR studies show that Fe(III)-TAML complexes become six-coordinated in water. Also, the expansion of coordination is energetically favorable. UV-visible Spectroscopy and EPR data propose that at higher pH (pH 10) the Fe(III)-TAML complexes form an aqua-hydroxo species. This is a result of proton dissociation from one of the axial water molecules.

Stability:     

The planarity of the ring typically relies on the position and nature of the substituents and size of the ring. The hydrolytic stability of the complexes decreases if four amide nitrogens are non-planar. Furthermore, slight changes in the substituents leads to major effects on hydrolytic stability. Kinetic studies have shown that an increase in hydrolytic stability is seen when methyl groups are replaced with fluorines on the tail of the complex. In other words, demetalation of Fe^III-TAMLs increases hydrolytic stability.

Reactivity and stability:

Using the appropriate reaction conditions, the rate constants for intramolecular degradation can be calculated and we can show that the design of both the head and the tail is critical for controlling the lifetime and reactivity of TAML oxidant activators. In order to create new green catalysts, understanding the activity-stability relationship is very crucial. It is very important for these catalysts to be completely decomposed after they have been used, this is so that the reactive catalyst does not get emitted as a component of an effluent stream.

Fe^IV-TAMLs:

Oxidation under different conditions shows a variety of high-valent forms of iron–TAMLs. These forms include Fe(IV)–TAML high spin (S= 2), intermediate spin (S= 1), and coupled spin (S=0) systems of μ-oxoiron(IV) dimers. Mossbauer and EPR spectra are used to analyze the framework of the spins.

High spin complex (S= 2)

This complex is an example of a fully characterized, stable, non-heme Fe(IV) complex with high spin configuration. The macrocyclic tetraamide ligand, stabilizes a five-coordinated Fe(IV) center with square pyramidal geometry that is stable under ambient conditions in dichloromethane solution and as a crystalline material. The Fe(III) complex x-ray structure shows low symmetry, where the amide nitrogen functional groups are significantly distorted from planarity. The Fe(IV) complex solid-state structure can be described as a distorted square pyramid with all the amide nitrogens in a plane and the iron above the plane.The Fe–N and Fe–Cl bond lengths are shorter in the higher iron oxidation state (Fe^IV) compared to lower iron oxidation state (Fe^III).

Intermediate spin complex (S= 1)

Based on whether the oxidation of the Fe(III) is metal-centered or ligand-centered there are two forms of Intermediate spin (S= 1) Fe–TAML complexes. Metal-centered oxidation yields S=1Fe(IV) complexes and ligand-centered oxidation leads to complexes where SFe= 3/2 Fe(III) site is antiferromagnetically coupled to a ligand radical which results in a total of S=1.

Ligand b	R	X
H4B	-CH2CH3	-H
H4DCB	-CH2CH3	-Cl
H4DMOB	-CH2CH3	-OCH3
H4B*	-CH3	-H
H4DMOB*	-CH3	-OCH3
H4DCB*	-CH3	-Cl
H4BF2	F	-H

Second 250 Words Contribution:

The two different types of Fe-TAMLS:

There are two different types of Fe-TAMLS, they are referred to as redox innocent ligands (H4MAC) as seen in Fig.1, and redox non-innocent ligands (H4BandH4B*) as seen in Fig.2.  Various characteristic features can be seen between these two types of Fe-TAMLS. The X-ray crystal structure of H4MAC (redox innocent) showed indistinguishable CO bonds at the 3 confidence level. Also, showed indistinguishable C-N bonds. The degrees of amide non-planarity could be indicated based on the dunitz amide values. From the deprotonated amide N-donors, the redox innocent ligand has very strong R-donor capacity and also has high resistance to oxidative degradation. These type of ligands have shown to stabilize rare high-valent transition metal centers (Fe^IV, Cr^V, Ni^III). However, Fe complexes of 5,6,5,6-ring system (numbers are referred to the number of atoms this includes the metal in each chelate ring) are hydrolytically sensitive, which results in a system of limited value for oxidation catalysis in water. As for the redox non-innocent ligand, the ligands respond electronically and structurally to changes in oxidation state. This showed that increased hydrolytic stability for a range of iron complexes could be achieved by preparing specific combination of ring size (5,5,5,6-TAML) ligands. The non-innocent ligands include two ligand sections referred to as the “head” and the “tail”. Changing any part of these sections results in changes in the properties of the complex. The selectivity and the lifetime of catalysts is affected from moderately changing the ‘‘head’’ substituents, and the lifetime and the rates of hydrolytic degradation is greatly affected from changing the ‘‘tail’’ substituents.

First 250 Words Contribution:

Fe-TAML structure

Consists of an iron atom in the center surrounded by four protein-like constituents made up of hydrogen, carbon, oxygen, and nitrogen. In the pre-catalyst forms of Fe-TAMLs, the central Fe_III ion (S=3/2) is bonded to the four, almost planar, deprotonated amide nitrogen atoms. Oxidation under different conditions forms a variety of high-valent Fe-TAMLs. Fe_III-TAML complexes are five-coordinated in the solid state and become six-coordinated in aqueous solutions.

Fe-TAML catalysts and its environmental applications

Fe-TAMLs are nontoxic, environmentally-friendly catalysts. They safely degrade stores of harmful pesticides by causing less harm to humans and farm animals. It takes about 1to10 parts per million of the catalyst in water in order to speed up oxidative reactions to commercially useful rates. Iron (III) TAMLs are highly active catalysts that function effectively at very low concentrations. Fe-TAMLs have the ability to rapidly breakdown the pesticide fenitrothion completely. In the United States, fenitrothion is mostly used in household ant and roach traps. Whereas, in countries like Europe and elsewhere, they spray it on fruits and grain crops, and use it to kill flies and other bugs. Fenitrothion is a harmful pesticide and must be neutralized wherever it is used. This harmful pesticide could be destroyed by mixing it with a water solution containing quantities of Fe-TAML catalysts and hydrogen peroxide. A great advantage of using the Fe-TAML catalyst is that the clean-up process won’t be an issue in areas where water is at a premium. Once one batch of the pesticide is broken down, the water being used can be recycled and used to treat the next batch.

Fe-TAML catalysts also have the ability to destroy two chlorinated pesticide agents (pentachlorophenol and 2,4,6-trichlorophenol) that pollute many water supplies. Iron-TAML catalysts used to destroy these pesticides were highly effective compared to any alternative treatments, and were successfully able to destroy the pesticides without producing toxic by-products.

TOPIC SELECTION:

For First 250 Words:

Biomimetic Fe(TAML) complexes:

Fe-TAMLS structure

Fe-TAML catalysts and its environmental applications

Cytochrome P450:

-isolation/catalytic rate

-Cytochrome P450 reductase-discuss Fe-S

If extra space left maybe adding details to ascorbate ferrireductase / Ferrichrome

Week3 Tasks - Info for Chromium (III) acetate

Properties of Chromium (III) acetate

• molecular formula: C₆H₉CrO₆
• molar mass: 229.128 g/mol
• m.p: >400 deg C
• b.p: 212° F at 760 mm Hg for aqueous solution
• solubility in water: 675 g/L at 20 deg C (pH 5)

Chromium (III) acetate

Chromium (III) acetate

Other information on Chromium(III) Acetate

The Pubchem catalog entry for Chromium (III) acetate

The Electronic Spectrum of Trinuclear Chromium(II1) Acetate

Exchange interactions in trinuclear basic chromium(M) clusters: Direct observation of the magnetic spectrum by inelastic neutron scattering

Crystal Structures of the Isomorphous Prototypic Oxo-Centered Trinuclear Complexes

References

Properties
Chemical formula	C6H9CrO6
Molar mass	229.128 g/mol
Melting point	>400 deg C
Boiling point	212° F at 760 mm Hg for aqueous solution
Solubility in water	675 g/L at 20 deg C (pH 5)

Nargas13/sandbox

Names
IUPAC name Chromium(III) acetate
Identifiers
PubChem CID	14012
Properties
Chemical formula	C6H9CrO6
Molar mass	229.128 g/mol
Density	1.56 g/cu cm at 22.95oC
Melting point	>400oC
Boiling point	212oF(at 760mm Hg) for aqueous solution
Solubility in water	675 g/L at 20oC, pH 5
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	Skin, Eye, and Respiratory Irritations
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Formula Practice:$\left({\frac {1}{2}}\right)d=\left({\frac {1}{2}}\right)\times \surd {\Bigl (}{\bigl (}x_{2}-x_{1})^{2}+{\bigl (}y_{2}-y_{1}{\bigr )}^{2}{\Bigr )}$

Copper coordination for 4 classes of copper proteins

Mechanism for carboxypeptidase A for carboxyprotein B, i) shows reaction via nucleophilic water and ii) shows reaction via anhydride.

Mechanism of LADH