In EXAFS and XPS-ray analysis, metal complexes surrounded with nitrogen and oxygen. In these case how can we find out that exact Metal-Nitrogen and Metal-Oxygen bonds ?
Help me please...
Hi Raj,
from EXAFS you determine the distances from a center atom to the nearest neighbor atoms. By choosing the right K-edge energy you can decide which type of center atom you want to have. So you can either take the metal atom (Co) or the N or the O atom. But the two latter ones have very low energy K-edges (N: 397eV, O: 533eV), so you have to use a vaccum system for your experiments and a synchroton or storage ring as radiation source.
For Co as center atom there is no real need for a vaccum system, but no need for a synchrotron. But from the EXAFS point of view you cannot really distinguish if you see a N or a O atom as neighbor atom, because their atomic number difference is only 1. So the 1/7 to 1/8 difference in Z and thus a small difference in backscatter amplitude will result more in a 'believe' than in an objective decision which neighbor you have.
So I think you have to go to the K-edges of N and O and having Co as backscattering neighbor of the electron wave in the EXAFS set up.
From the Nitrogen point of view you should mainly see the Co atoms as neighbor because of its very high atomic number compared to that of N and O. The same holds for Oxygen as center atom.
A little drawback comes up: the energy difference in the K-edge energies of N and O is only about 136eV. So I suspect that in the O-edge EXAFS you will have residual EXAFS from the N edge superimposed. You have to take care about this.
Mr. Kumar,
In which context you have used 'how'?! - Directly! Often with good accuracy.
Dear Raj,
The small difference in Z between N and O atoms will give highly similar scattering strengths making it impossible to distinguish between N and O scattering contributions. The simplest way to reveal the identity of the ligands would be to perform additional valence-to-core (VtC) X-ray emission spectroscopy experiments. This technique is able to distinguish elements with highly similar atomic numbers such as N and O (or a mixture). The high sensitivity arises from VtC transitions due to relaxation of an electron to the metal 1s hole from the ligand 2s (Kβ’’ signal) and 2p (metal 4p) orbitals (Kβ2,5 signal).
Hi Amir, you are able to identify N and O and their relative amounts; but are you able to provide the Co-O and Co-N bond length with your technique. I do'nt think so. I may be wrong.
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