[Ifeffit] Regarding a fit for Fe(OTf)2

Wed Dec 3 10:10:32 CST 2014

Hi Pushkar,

This is a difficult question for me to answer in a specific way
because you have assumed (wrongly, in my case) that the reader would
know what "OTf" means and to have a sense of what kind of structure
you are anticipating.

You showed a fit and gave some of the statistical results.  Nothing
seems obviously wrong.  The fit looks reasonable and the four fitting
parameters seem defensible in the sense of having reasonable values
and reasonable error bars.

Your central concern seems to be that you were expecting one thing and
found a different thing in the fit.  I am more skeptical of the sample
than of your ability to run the software.

  * Do you have any evidence that the sample you measured is the thing
    you intended to measure?  That is, do you have XRD or some other
    measurement to verify its identity?  (The label of the bottle that
    you took it from does not constitute "evidence"!)

  * Do you have any evidence that there is S in your sample?  That is,
    do you see a S peak in the XRF spectrum?

  * You mentioned something about the reactivity of your sample.  Do
    you have a measurement indicating that the sample on which you
    measured EXAFS is in the state that you want to measure?  For that
    matter, do you know that the sample is stable under the X-ray beam?

  * You state that the bottle said "anhydrous".  Is it hygroscopic?
    Did you take great care to avoid contact with air as you were
    preparing and measuring the sample?  You suggest that you did not,
    so it seems reasonable that it could have sucked water out of the
    air -- lots of things do.

B

On 12/02/2014 08:22 PM, pushkar shejwalkar wrote:
> Dear All,
>              I am experiencing problem during my fit for Fe(OTf)2
> anhydrous. The problem is as follows.
> I collected the data and used a model to fit. The fitting values and
> other technical information is as below. The basic problem is Fe(OTf)2
> in anhydrous condition is probably not cyrstalline because of which
> there are no crystal data available. Although .cif file is available for
> hexahydrate and tetra acetonitrile. But obviously it is not directly
> useful as I am looking for Fe(OTf)2 only. I used hexahydrate for
> fitting, and the fit information is given. Is this fit acceptable?
>
> *Now two questions*
> 1) Why do I not see any scattering or peak for Fe-S. I expected S to be
> a strong scatterer and would  show a peak. Under given circumstances it
> looks like Fe is all surrounded by water and no triflate is present near
> Fe at all. Is this assumption even make sense (when the bottle said
> anhydrous) The bottle was not kept under inert condition (and its my
> fault), but does it mean Fe(OTf)2 is so hygroscopic and that it can
> actually form such hexahydrate to the full extent?
> OR there is some inherent problem with my fitting and collection itself.
> I used RBKG=1.0
>
> 2) Is anybody working on Fe(OTf)2 and had such or any other problem
> indicating that Fe(OTf)2 by itself is a bad choice of precursor because
> of its reactivity. Also any comments on purification method etc. does
> anybody know if crystal structure is available for Fe(OTf)2 anhydrous? I
> could not find it on the quick search or on CCDC. Any other site where I
> can get crystal data and .cif information?
>
> Thank you very much for all the help, I hope the question is asked
> appropriately and all the other information is provided, however, if
> anybody needs any other information please let me know.
> Thank you in an anticipation
> Best
> Pushkar
>
>
> Independent points          : 16.1250000
> Number of variables         : 4
> Chi-square                  : 7324.9401796
> Reduced chi-square          : 604.1187777
> R-factor                    : 0.0195782
> Measurement uncertainty (k) : 0.0001264
> Measurement uncertainty (R) : 0.0004142
> Number of data sets         : 1
>
> guess parameters:
>    SO                 =   1.06525455    # +/-   0.05504541     [1.00000]
>    delE               =  -2.32587026    # +/-   0.59606221     [-2.77870]
>    delR               =   0.00911122    # +/-   0.00503027     [-0.02322]
>    ss                 =   0.00706809    # +/-   0.00071967     [0.00300]
>
> Correlations between variables:
>                  delr & dele               -->  0.9154
>                    ss & so                 -->  0.9023
> All other correlations below 0.4
>
>   name        N       S02     sigma^2   e0     delr     Reff     R
> =========================================================================
>   O1.1      6.000   1.065   0.00707  -2.326  0.00911  2.09150  2.10061
>
>
> --
> Best Regards,
> Pushkar Shejwalkar.
> Post-doctoral -Researcher,JSPS Fellow
> Hokkaido University,
> Sapporo,
> Japan
> Inline image 3
>
>
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-- 
  Bruce Ravel  ------------------------------------ bravel at bnl.gov

  National Institute of Standards and Technology
  Synchrotron Science Group at NSLS-II
  Building 535A
  Upton NY, 11973

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