[Ifeffit] Coordination number

[Anatoly Frenkel]

This is not quite accurate: the coordination number measured by EXAFS is the
TOTAL number of closest neighbors per TOTAL number of absorbing atoms. If
the sample is a single phase, these two definitions are the same. If the
sample is heterogeneous, e.g., some percentage x of nanoparticles and the
rest (1-x) percent - low molecular weight complexes of the same metal, EXAFS
will measure coord. number of metal-metal bonds to be much lower than you
expect in the particle of a given size and structure.

The scaling factor can be found here:
http://pubweb.bnl.gov/users/frenkel/www/Pd-SUNY/pd-suny.pdf

Anatoly


-----Original Message-----
From: ifeffit-bounces at millenia.cars.aps.anl.gov
[mailto:ifeffit-bounces at millenia.cars.aps.anl.gov]On Behalf Of Stefano
Ciurli
Sent: Thursday, November 23, 2006 1:38 PM
To: XAFS Analysis using Ifeffit
Subject: Re: [Ifeffit] Coordination number


Hi Juan,

I am not sure why you say that the question is
polemic. I will give you the definition that a
coordination chemist would give:

the coordination number is the number of closest neighbours.

But maybe I do not understand the question

Regards
Stefano

>I have a simple question but I am afraid it is polemic. Why people
>always calculate coordination numbers and bond distances and how?
>I have an e-mail where Bruce described perfectly how to calculate the
>coordiantion number for the first shell. But,...if I have bimetallic
>catalysts or/and a mixture of structures with several close paths
>(similar Reff), then coordination number is an average number? I am not
>very sure how to calculate them in Artemis with SO2 and standards.
>
>Thank you very much
>
>Best regards,
>JA
>
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--
____________________________________________

Stefano Ciurli
Professor of Chemistry
Laboratory of Bioinorganic Chemistry
Department of Agro-Environmental Science and Technology
University of Bologna
Viale Giuseppe Fanin, 40
I-40127 Bologna
Italy
Phone:	+39-051-209-6204
Fax:	+39-051-209-6203

"Fatti non foste a viver come bruti,
ma per seguir virtute e canoscenza"
Dante Alighieri - Inferno - Canto XXVI

"Ihr seid bestimmt, nicht Tieren gleich zu leben,
Nein, Tugend zu erringen und Erkenntnis"
"Ye were not form'd to live the life of brutes,
But virtue to pursue and knowledge high"

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