Hi Matt, Thank you for the explanation. In this case, comparing oxides provides only a rough approximation of the oxidation states. Using both oxides and sulfides would incorporate the contribution of covalency and lead to inaccuracies. What
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Hi Matt,

Thank you for the explanation.

In this case, comparing oxides provides only a rough approximation of the oxidation states. Using both oxides and sulfides would incorporate the contribution of covalency and lead to inaccuracies. 

What about utilizing the pre-edge mixing oxides and sulfides? I have a concept that is more related to the symmetry of the site, although this understanding also originates from oxides.

Best regards,



On Fri, Feb 28, 2025 at 11:54 PM matt.newville@gmail.com <matt.newville@gmail.com> wrote:

Hi Benito,

 

The energy of the sharp rise (ie, the energy of the empty metal 4p states) is a simple measure of the “charge state” or “oxidation state” of a metal.   To be clear, for a particular ligand type (say, oxygen), the energy of 4p states, and so also the energy of the main rise in mu(E), will change systematically with energy.  But if you change the ligand, and the covalency/ionicity of the bond, that will also move the energy of the metal’s 4p states.  Metal sulfides are much more covalent than metal sulfides, and many are semi-metallic.  If I understand correctly, titanium disulfide is used because it is electrically conductive.

 

OTOH, titanium dioxide will have a band gap of a couple of eV. That “band gap” is strongly correlated with the edge shift.

 

Again, the energy of the “main edge” is just not a simple measure of “oxidation state”, especially if the ligand is not oxygen. 

Using the term “oxidation state” for a sulfide is not going to give you much insight.

 

--Matt

 

 

From: Benito Melas <metal.cnea@gmail.com>
Date: Friday, February 28, 2025 at 7:58 AM
To: matt.newville@gmail.com <matt.newville@gmail.com>
Subject: Re: [Ifeffit] Question about Ti edge

Hi Matt,
As you mentioned, "for the transition metals, there will usually be a sharp rise in mu(E) at the energy."
In the case of LTS, however, this sharp rise occurs at lower energies than in TiO2, which raises concerns regarding the claim that both compounds exhibit the same oxidation state.
Thank you for your continued dedication to enlightening our community.
Best regards,

 

 

 

On Fri, Feb 28, 2025 at 3:46 AM matt.newville@gmail.com <matt.newville@gmail.com> wrote:

Hi Benito,

 

>  The authors claim

>> The peak position for LTS-213 is approximately 4970 eV, which agrees well with that for rutile TiO2 with a valence of titanium species in the 4+ oxidation state.

 

> Should we use the pre-edge to determine the oxidation state? Is it reliable, or should we use E₀ and compare it with references of well-known oxidation states?

 

Many people use pre-edge peaks of transition metals for reliable analysis of metal oxidation states.   

 

E0 is sort of poorly defined term.  For the transition metals,  there will usually be a sharp rise in mu(E) at the energy of the metal’s own 4p electrons – the “main edge”, though this can sometimes be tricky to identify precisely, and sometimes has structure (as TiO2 does – slightly different for its different forms).

 

>> In addition, TiS2, in which titanium is also in the 4+ oxidation state, shows pre-edge peaks at 4968–4971 eV. (21) Considering the titanium oxidation state

>> in the raw materials, the stability of the titanium species, and the XANES results, the oxidation state of the titanium species in LTS-213 is likely to be 4+.

> The second conclusion is even more unclear.

What confuses me there is “TiS2 is in the 4+ oxidation state”.  Titanium disulfide is not oxidized at all - it is bound to sulfur.   Its charge state could be 4+, and many chemists use “oxidation” to mean the transfer of charge to and from a metal, whether this is done by oxygen or not.  For XANES, the ligand species matters.   K-edge XANES shows the energies of the unfilled p states at the center of the Ti atom, which will be very different for Ti-S (more covalent) and Ti-O (more ionic) bonds.

--Matt

 

 

From: Benito Melas via Ifeffit <ifeffit@millenia.cars.aps.anl.gov>
Date: Thursday, February 27, 2025 at 7:28 AM
To: ifeffit@millenia.cars.aps.anl.gov <ifeffit@millenia.cars.aps.anl.gov>
Cc: Benito Melas <metal.cnea@gmail.com>
Subject: [Ifeffit] Question about Ti edge

Hi all, I was following this article about Li2TiS3 https: //pubs. acs. org/doi/full/10. 1021/acs. inorgchem. 4c03864 and found this Ti edge XANES figure The authors claim The peak position for LTS-213 is approximately 4970 eV, which agrees well with

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Hi all,

I was following this article about Li2TiS3


and found this Ti edge XANES figure


The authors claim

 

The peak position for LTS-213 is approximately 4970 eV, which agrees well with that for rutile TiO2 with a valence of titanium species in the 4+ oxidation state.

 

Should we use the pre-edge to determine the oxidation state? Is it reliable, or should we use E₀ and compare it with references of well-known oxidation states?

 

In addition, TiS2, in which titanium is also in the 4+ oxidation state, shows pre-edge peaks at 4968–4971 eV. (21) Considering the titanium oxidation state in the raw materials, the stability of the titanium species, and the XANES results, the oxidation state of the titanium species in LTS-213 is likely to be 4+.

 

The second conclusion is even more unclear.

Would you help me see if I am missing something in my understanding of oxidation states using XANES?

 

Best, B.