The position of a peak in XPS is affected by the initial binding energy state of the electron in the orbital. When something external to the atom changes the binding energy state of the electron in the orbital, the result will be a shift in the XPS peak position. Ligands pull or push electrons from/to an atom. That changes the effective charge on the atom. That changes the binding energy of the electron in orbitals. That shifts the XPS peak. Other factors can work in the same way. The coordination number effect ... I cannot say for certain whether it will or will not affect the initial state. Others may have greater insight.

The position of a peak in XPS is also affected by factors called final state effects. These have to do with what happens as the hole that is left when the electron leaves relaxes back to its ground state. I can image that coordination geometry has some subtle final state effect. This is equivalent to the changes that happens as one goes from individual atoms to atomic clusters to bulk materials. The final state is dissipated differently in each system.

Finally, metallic Ni and oxidized Ni have distinctly different peak positions.

The position of a peak in XPS is affected by the initial binding energy state of the electron in the orbital. When something external to the atom changes the binding energy state of the electron in the orbital, the result will be a shift in the XPS peak position. Ligands pull or push electrons from/to an atom. That changes the effective charge on the atom. That changes the binding energy of the electron in orbitals. That shifts the XPS peak. Other factors can work in the same way. The coordination number effect ... I cannot say for certain whether it will or will not affect the initial state. Others may have greater insight.

The position of a peak in XPS is also affected by factors called final state effects. These have to do with what happens as the hole that is left when the electron leaves relaxes back to its ground state. I can image that coordination geometry has some subtle final state effect. This is equivalent to the changes that happens as one goes from individual atoms to atomic clusters to bulk materials. The final state is dissipated differently in each system.

Finally, metallic Ni and oxidized Ni have distinctly different peak positions.

Hello,

on the website http://www.xpsfitting.com/

you can get some hints. Look for the example "Copper". There it is shown the complexity of the photoionization prozess.

Dear David,

I would suggest to read the following articles: http://www.sciencedirect.com/science/article/pii/S0020169300806052

http://chempedia.info/info/34025/

They might help you with the "understanding". There are plenty of other articles dealing with this phenomenon, especially: 

http://www.xpsdata.com/frmain.htm

Ask for this handbook at your library it would help you definitely. This is probably the largest collection of spectra.

Pavel

Hi David

In terms of electronegativity shifts etc, you seem to have a grasp on that and also Jeffery's reply is useful for you.

In terms of Different environments for BE shifts this can happen, although the magnitude can be small.  Other things to look out for are changed in multiple splitting, especially for high-spin vs low-spin complexes for example.  SOme examples drealing with such phenomena are (albeit for Fe and Co compounds)

https://doi.org/10.1016/0009-2614(76)80360-0

https://doi.org/10.1016/0368-2048(83)80028-0

http://www.surfacesciencewestern.com/pdf/04-006_apg.pdf

http://iopscience.iop.org/article/10.1088/0022-3719/14/25/010/pdf

A (non Ni Oxide) references for Ni which may be a good start for you is:

http://dx.doi.org/10.1063/1.446359

Dear Jeffrey J Weimer, Dietmar Hirsch, P. Dytrych and David J. Morgan ,

Indeed I appreciate your respective contribution to the question raised. I now have almost unlimited information on the subject.  Thank you all for your time and contributions.

David, I wish I see Professor Jeffrey. He is a distinguished scholar.