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
*Date: *Friday, February 28, 2025 at 7:58 AM
*To: *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
*Date: *Thursday, February 27, 2025 at 7:28 AM
*To: *ifeffit@millenia.cars.aps.anl.gov
*Cc: *Benito Melas
*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
https://urldefense.us/v3/__https://pubs.acs.org/doi/full/10.1021/acs.inorgch...
https://urldefense.us/v3/__https:/pubs.acs.org/doi/full/10.1021/acs.inorgche...
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.
Benito Melas